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THE LIBRARY 
OF CONGRESS 

WASHINGTON 



Entered, according to Act of Congress, in the year 1876, by 

CLAXTON, KEMSEN & HAFFELFINGER, 
in the Office of the Librarian of Congress, at Washington. 



k* DlAXV£i 



J. FAGAN & SON, fesSkJU 



STERE0TTPER8, PHTLAD'A. 



EVERY-DAY REASONING; 



GR, THE 



SCIENCE OF INDTJCTIYE LOGIC. 



BY 

Rev. GEO. P. HAYS, D.D., 

PRESIDENT OF WASHINGTON AND JEFFERSON COLLEGE. 



ISI/G9S 



PHILADELPHIA: 
CLAXTON, EEMSEN & HAFFELFINGER, 

624, 626 & 628 Market Street. 
1877. 



jj^iaty t\h Iftkw 



TO 

MY CHERISHED FRIEND S, 

THE YOUNG MEN WHO HAVE BEEN STUDENTS OF WASHINGTON 
AND JEFFERSON COLLEGE DURING THE YEARS 1871-1877 
(INCLUSIVE), .AND ESPECIALLY TO THE GRADU- 
ATING CLASSES DURING THAT PERIOD. 

G. P. H. 



PREFACE. 



THIS work is offered to teachers as an aid in setting before 
their pupils the principles of Inductive Logic. As our 
reasoning is inductive rather than deductive in daily life, 
it is important that the young should -know at least the 
methods and tests. No great claim to originality is made, 
as no effort was put forth to attain it. Everything within 
reach has been examined, in order to gain additional light ; 
and much that was desirable was left out, in order to keep 
the book within such bounds that it could be easily mastered 
by average students in a single session. ( Some important 
matters, and some especially clear illustrations, have been 
repeated in different connections, in the belief that repetition 
aided the memory. The design in preparing the work was 
not merely to offer a text-book to schools, but also to pro- 
vide a convenient manual for men and women in their pro- 
fessional and daily life, wherein they might find suggestions 
for making their experiments, reaching their conclusions, 
and testing the correctness of the same. Under the title 
Every-Day Keasoning, an outline of the thought has 
been very frequently delivered as a lecture; and the favor- 
able reception accorded to the subject in that form has led 
to the hope that greater usefulness would be attained by its 
publication in this form. Of course, the difference of cir- 
cumstance and aim will account for the difference of style. 

Washington and Jefferson College. 



CONTENTS. 



PAGE 

Preface . v 

Introduction ix 



PART FIRST. 

TRUTH. 

Truth vs. Falsehood .-... 13 

Mixed Truth and Falsehood 16 

The Importance of Truth 17 

Necessary and Caused Truth. 18 

Reasoning on Necessary Truth 21 

Reasoning on Caused Truth, , 22 

Classification ' 23 

Cumulative Reasoning ..:... 25 



PART SECOND. 

CAUSES. 

Nature's Offering 29 

Nature's Laws ... 30 

Efficiency of Causes ; 34 

Causes Defined 39 

Difficulties of Identifying Causes 42 

Selection of Facts 4G 

vii 



Vlll CONTENTS. 

PART THIRD. 

METHODS OF INDUCTION. 

PAGB 

General Statement 51 

Method of Agreement 53 

Method of Difference 58 

Method of Besidues 65 

Method of Concomitant Variations ... 70 

Four Methods Illustrated 76 

Classification by the Four Methods 87 

Analysis 92 

Questions of Inductive Logic 96 

Final Causes or Design 102 

PART FOURTH. 

STEPS IN INDUCTION. 

Stating the Question 107 

Gathering the Facts Ill 

Detection of Law 115 

Verification — Explanation of Facts 120 

Eule of Harmony 123 

Eule of Simplicity 129 

Eule of Concurrence 135 

Eule of Sufficiency? 141 

Eule of Prediction 148 

Jhe Interpretation of Documents 155 

The Art of Debate 162 

Index 169 



INTRODUCTION. 



THE irresistible reason for keeping arithmetic as a study 
in every common school is, that every person must keep 
all their accounts by it. If they are not able to perform its 
simpler operations correctly, they are not able to take care 
of their own rights. They are liable to be both intention- 
ally and unintentionally cheated. In order, therefore, to fit 
them, in any sense, for their future lives, our children are 
taught these arithmetical rules. They are rightly enough 
compelled to learn the multiplication table, before they have 
any true idea of what it means, -or any conception of the 
many uses they will afterwards have for it. 

These same things are just as true of reasoning as of 
arithmetic. Everything we do is done for a reason. We 
do not need arithmetic for every conclusion to which we 
come. We cannot come to a conclusion without more or 
less of a reasoning process. The old adage, of children 
learning to dread the fire, is reached by the method of agree- 
ment. The child dreads this fire, because it agrees in ap- 
pearance and otherwise with the fires by which it has here- 
tofore been burned. This is exactly inductive reasoning. 
The same thing will be true of the child in all its after life. 
It will plan its business, and seek its pleasures, by reasons 
which are subject to, and may be tested by, the methods of 
inductive logic. Every merchant at his counter, every me- 
chanic at his trade, every farmer in his fields, every house- 
wife at her work, every cook at the stove, in arranging each 
step of their daily duties, will decide on what they will do, 
because they either wish to attain what they have been able 



X INTRODUCTION. 

to accomplish in that way before, or they will try some new 
plan, because they want to avoid some evil, or danger, or 
apparently needless labor. If their reasoning is correct and 
their facts reliable, they may expect success; if they are 
mistaken as to the, facts, or incorrect as to their inductions 
from them, the/ will almost certainly fail. Masses of men 
are bankrupt, jecause they bought at the wrong time and 
sold at the wrong time. Their intentions were honest, but 
their reasonings were fallacious ; and no integrity of purpose 
will save a man, when he misses his facts, and reasons badly 
on such as he may have. When now life and its oppor- 
tunities come to us but once, and a blunder, though some- 
times it may be rectified in the future, irreparably loses for 
us the present occasion, of what supreme importance is it, 
that we should, as far as possible, save ourselves from mis- 
takes ! Every day we will do what we will do, because we 
think, by the course we adopt, we will attain our desired 
ends. If in that course of reasoning we are wrong, we will 
fail, and ought to. By as much, therefore, as the number 
of times we act on our own judgment exceeds the number 
of times we need to employ arithmetical computation, by so 
much is a knowledge of inductive logic of more practical 
use than arithmetic. 

Geography is everywhere taught, and children's minds 
are burdened with the names of innumerable capes and 
rivers they will never see, ancl of whose existence, if they 
should be ignorant all their lives, they would perhaps lose 
but little. It is not creditable either to a child's parents or 
teachers, that it should be allowed to grow up unable to 
speak its mother tongue with considerable accuracy. Many 
people, however, who use bad grammar, and know but little 
geography, succeed finely in business, because they can 
reason correctly. Thus they make no mistakes in trade, 
and waste neither time nor money on foolish projects, with 
all their bad grammar. 



INTRODUCTION. XI 

The great difficulty, however, with inductive logic is, to 
make it so plaiu that its application to every- day life will be 
obvious. If it could be so simplified and adapted to common 
affairs, that its relation to daily business could be seen as 
directly as that of arithmetic or grammar, there would be 
no serious obstacle in securing for it a similar place. But 
even if no book fully meeting the case has yet been pro- 
vided, it is worthy of consideration whether it is not better 
to study a poor book than none at all. By no possibility 
can any one escape the necessity of every-day reasoning ; 
and the successes or failures that will come from their good 
or bad logic, will come upon their own heads, study or no 
study. 

In this work, Part First is devoted to a discussion of the 
different kinds of truth and reasoning ; Part Second treats 
of the materials furnished us on which to reason ; Part Third 
explains the four methods and the questions inductive logic 
is adapted to answer ; Part Fourth gives the steps to be fol- 
lowed and the five tests by which true conclusions may be 
known to be true, and false ones detected as false. Some 
practical matters are then added, not immediately connected 
with this subject, but belonging to its field rather more than 
to any other included among text-books. All readers, as 
well as all students, are strongly advised to commit to mem- 
ory the names of the four methods and the five tests, and 
then so study them that their names will readily suggest 
their application. 



EVERY-DAY REASONING. 



PART FIRST. 
TRUTH. 

TKUTH vs. FALSEHOOD. 

TRUTH is, what is, as it is. Otherwise defined, truth is 
the characteristics and relations of things, individually, 
collectively, and relatively. Truth thus includes not merely 
the conditions of things considered alone, but it is limited 
and confined by the relations of things among themselves. 
The opposite of truth is falsehood, which is an assertion that 
certain things, characteristics, or relations exist when they 
do not. By comparing and contrasting these two, a more 
exact knowledge of both will be obtained. 

First Distinction. — Truth is in things. Falsehood is never 
in the things, but only in the conceptions of them, or the 
statement of those conceptions in words. There are thus 
three places where truth may be found, and only two for 
falsehood. Truth exists first in the things themselves. Then 
this truth may be correctly perceived by the mind. It may 
then be stated in words, as it is thus correctly perceived by 
the mind. -For example, two and two are four. We see 
this and say so. The ship has three masts. We count them, 
and state the fact. The horse is a quadruped. We notice 
this when we see one, and so record it. But if we say two 
2 13 



14 EVERY-DAY REASONING. 

and two are five ; the ship is feathered ; the horse chews the 
cud ; these are not true. They have not, however, changed 
the relations of numbers, the character of the ship, or the 
nature of the horse. Things themselves never lie. Men 
may misunderstand them, and they may consciously or un- 
consciously state that which is not true concerning them ; 
but the truth is not affected either by their misapprehension 
or misstatement. It remains the same, regardless of the im- 
pressions men take up concerning the matter. Truth, there- 
fore, is in things themselves, and may be perceived by the 
mind, and then stated in words ; but falsehood is only 
found in men's conception of things, or their statements in 
words. 

Second Distinction. — Truth is true without regard to man's 
action, and so is true before its discovery by the human 
mind. Our perception of it affected us, but it did not affect 
it. It was just as true before, as after, men came to the 
knowledge of it. Gravitation was just the same before the 
discovery of its laws by Newton, that it has been since. It 
acted just as powerfully, and in just the same way. The 
stones fell, and stars moved, and bodies weighed, just as they 
did afterwa'rds. After we discover truth, we are enabled to 
avail ourselves of it in the accomplishment of our purposes ; 
but the truth was there before. Steam was as ready to do 
its work before the days of \Vatt as since, only we could not 
use it. The development of geometry in no way affected 
the relations of lines or angles. Falsehood, on the other 
hand, never exists until after men have acted. As it exists 
only in our conceptions or our statements, of course it could 
only come into being by the action of our minds. It was a 
great error to say that two pounds of lead would fall to the 
ground twice as fast as one pound; but such a thought 
never had any existence until some mistaken philosopher 
made the assertion. The indications were all the other way, 
until Ananias and Sapphira asserted that what they gave 



TRUTH. 15 

the apostles was the whole price for which they sold their 
land. It is thus left for the action of finite mind to bring 
all falsehood into being. 

Third Distinction, — Truth is always consistent with itself, 
so that each separate truth is consistent with every other 
truth. There is no such self-consistency and harmony in 
error. Falsehoods are not only at war with truth, but they 
wrangle and fight with each other. Every proposition of 
geometry is consistent with every other proposition. Every 
law of nature harmonizes with every other law. Truths are 
not only consistent when occurring at the same time, but 
they are the same in all time. When we have met with 
them once, we always find them returning the same. Even 
when they seem to contradict, we are sure that further in- 
quiry will reveal the secret of the apparent contradiction, 
and show that, instead of being a real contradiction, it is 
only a further proof of their fundamental harmony. False- 
hoods and errors, however, cannot be reconciled. Their 
contradictions are obstinate and without remedy. They are 
Ishmaelites. Each one is against every other, and all the 
others against it. The reason of this is plain. They come 
from finite mind, not from nature; thus there is no uni- 
form cause underlying their existence. They spring up out 
of men's mistaken notions, or their misleading words. If 
there is, therefore, consistency and harmony, — as there is 
sometimes among a few of them, — it is not the result of 
nature, but of design. Hence the proverb, that "liars 
should have good memories." Lacking this, they contra- 
dict themselves, and so disclose their falsehoods. History 
scarcely offers an instance of a fraud that could not be de- 
tected by its contradictions, while almost every page is 
marked by truths whose discovery was more or less due to 
search suggested by apparent inconsistencies, which were 
resolved by the new discoveries. 



16 E VERY-DAY REASONING. 

MIXED TEUTH AND FALSEHOOD. 

Truth and falsehood, or error, although thus radically- 
different, are not so opposed that they may not be mingled 
together. The truth in things is indeed unmixed with error, 
but a large part of men's observations have somewhat of 
truth, and somewhat of error in them ; and it is often very 
difficult so to state even true views, that no mixture of error 
shall be allowed to be hidden under our words. A witness 
is testifying as to what he saw of a quarrel, and affirms that 
he saw the prisoner strike the wounded man with a weapon. 
The truth was, he saw the prisoner in the melee with a knife 
in his hand, brandishing it over his head, and inferred that 
he inflicted the wound. The wound, however, was made 
with a dagger, sharp-pointed, but with no side edges ; and 
as there was but one wound, it was clear that the knife was 
not used at all. Both his observations and his statements 
had a mixture of truth and error. Many times the most 
difficult and delicate task is to separate this truth from 
falsehood, and much discipline is needful to enable us to 
recognize just what we do see, and limit our statements to 
the things thus actually seen. All falsehoods are by no 
means intentional, but they are just as misleading as if they 
were. An intention to state the truth no more makes an 
error true, than an intention to see correctly will remedy de- 
fective vision. An honest error may be just as fatal as a 
premeditated lie. A minister gave his wife poison when he 
intended to give her medicine. The fact that it was given 
in love could not save her life. No purpose, however pure, 
can transform error into truth. We must, therefore, inquire 
into the ability as well as the integrity of those who furnish 
us our facts, before we decide on their credibility. We can- 
not for ourselves verify all the facts on which we must 
reason, and so must take much furnished by others; and 
great care and ability will be required to separate the wheat 
of truth from the chaff of error with which it is mingled. 



THE IMPORTANCE OF TRUTH. 17 

THE IMPOETANCE OP TKUTH. 

t It is impossible to rate at too high a value this knowledge 
of the truth. The successes and failures, the encouragements 
and disappointments of life, are mainly attributable to want 
of correct information, and inability to draw correct conclu- 
sions frffm the information we have. If we proceed on false 
grounds, we are not to hope that nature will change, to re- 
lieve our defects. Having received the endowments of mind 
for the very purpose of discovering the true, and separating 
it from the false, a neglect to use these intellectual gifts 
properly is a crime that deserves the failures and mistakes m 
by which, in the course of nature, it is punished. The ex- 
perience of alh ages has taught the wisest of mankind to 
esteem the truth very highly. No patience or perseverance 
is considered in any measure unrequited, if thereby any 
grain of truth is added to human knowledge. The very 
first prerequisite to entering on investigation, therefore, is a 
singleness of mind that will accept any truth that may 
reveal itself, however it may contradict some previous 
notions. There is required a like readiness to discard any 
error, however it may have been cherished, the moment its 
character is detected. No error is valuable. All truth is 
priceless, and no man has any claim to be called a true 
thinker, who rebels against giving up any error at the de- 
mands of the truth. The truth always issues in the right, 
and error, however prosperous for a time, can only come to 
ultimate grief. Nature, and the God of nature, will at last 
be found supreme, and their truth vindicated. In all ages, 
scholars and philosophers have exhausted their power of 
language in laudation of truth, and the Son of God, as if 
to emphasize its importance, called himself " the way, the 
truth, and the life." Truth is our only guide to safety, and 
if, adopting error, we escape folly and peril, it is by acci- 
dent. 

2* B 



18 EVERY-DAY REASONING. 

NECESSAKY AND CAUSED TKTJTH. 

Truth may be divided into two departments, according .to 
the character of the subjects with which it has to do. One 
of these divisions is called necessary truth, and the other 
caused truth. The essential difference is indicated by the 
names necessary and caused. The relations of space and 
number are illustrations of necessary truth. The angles 
made by two intersecting straight lines in the same plane 
are not equal to four right angles, because any will made 
them so. It could not be otherwise. Two and two are four, 
I always and everywhere. It is not so with some other things. 
Thus, the builders might have made a ship with four or five 
masts, if they had so pleased. The Creator might have 
made the horse to chew the cud, as well as the cow and 
the sheep. These last are, therefore, not necessary truths, 
but caused truths. This leads us to notice a second dis- 
tinction between these two kinds of truths, namely, that 
caused truth depends on some will, while necessary truth 
does not. No volition could make two and two ten, or 
construct six right angles by any number of straight lines, 
intersecting each other at the same point in the same plane. 
Volition can have no influence on necessary truth ; it exists 
as it is, by its own necessity. On the other hand, all caused 
truth exists as the result of volition ; otherwise it would not 
exist at all. If the builders had not done their work, there 
would have been no ship ; if the Creator had so pleased, the 
world might have been made, and never a horse appeared 
on it; or the horses that were on it might all have had 
horns. What was, and how it was to be, depended on his 
determination. How long it shall be true also depends on 
will. I have built my house, but it depended on my will 
when I should build it, and it depends on my will how long 
it will last. I may, if I please, tear it down to-morrow. It 
exists, like all caused truth, as we might say, by sufferance. 



NECESSATvY AND CAUSED TRUTH. 19 

It was produced by causes, and causes can destroy it. The 
house will last so long as it is not taken down, or destroyed 
by fire, or tempest, or decay. So geology tells us of ani- 
mals, not now extant, and other convulsions may so change 
the face of the earth as to destroy some kinds of animals 
altogether, and it may be occupied by others, as different 
from any now as the elephant js different from the mega- 
therium. Caused truth is thus comparatively temporary. Its 
existence and present modifications are of recent origin, and 
will not, in any event, remain long unchanged: It is other- 
wise with necessary truth ; it is unchangeable. As it exists 
of necessity, it must, of course, be eternal. Two and two 
have always been four, and always will be. No cause 
made this so, and no cause can change it, so that two and 
two would be anything else than four. It is identical and 
invariable. We have thus three points of distinction be- 
tween necessary and caused truth. The first is that from 
which each division takes its name. One is necessary, and 
the other is caused. Again, caused truth depends on voli- 
tion, while the other does not. So, thirdly, necessary truth 
is eternal, while caused truth is temporary. 

With these three points of difference, there is one point 
wherein there is no difference. Both are equally true. Be- 
cause a thing which is true now was not true last year, and 
may not be true next, does not in any way invalidate its 
present verity. Caused truth, while it is true, is just as true 
as any necessary truth can be. It is no more certain that 
two and two are four, than that Napoleon was defeated at 
Waterloo, or that Washington was the first President of the 
United States. This is important, in view of the fact that 
often words and phrases are used to designate caused truth, 
which seem to carry under them an implication of some un- 
certainty. Thus the adjectives experiential, contingent, and 
probable, are used in speaking of it, or of the evidence by 
which it is proved ; and these are set over against, and con- 



20 EVERY-DAY REASONING. 

trasted with, such words as self-evident, axiomatic, and de- 
monstrative, as applied to necessary truth, and reasoning on 
it. This use of terms is apt to mislead us. The name 
caused truth is better, for the reason that after the causes 
have once produced their effect, the existence of that effect 
is just as certain as any truth is, and may be unhesitatingly 
relied on, so long as it lasts. With reference to very much 
of this caused truth, such as the events of history, it has 
passed out of the reach of change, and can, therefore, be 
no more doubtful. No future event can destroy the fact 
of Napoleon's overthrow, or substitute another name for 
Washington's as the first President. The channel of the 
Mississippi may be changed by the water wearing for 
itself new courses, and the great cities of to-day may be- 
come ruins, as many of the great cities of the past are now 
in decay. Some forms of caused truths are thus liable to 
change. The element of time must, therefore, be carefully 
noted ; for while a truth may not continue to be true as a 
constantly present truth, yet if it ever has been true, no 
change can destroy the fact that it was true at that time. 
Attention is, therefore, to be given to this point in every ' 
statement, whether it makes its assertion as a present and 
continuing fact, or as a fact at a definite time in the past. 
If it is true, nothing can be more true. There may be, as 
we shall see, a difference in our assurance of its truth ; but 
even in this respect, concerning a large part of caused truth, 
the assurance and certainty are just as absolute and positive 
as they can be in regard to any necessary truth. There 
may be great uncertainty as to the authorship of the letters 
of Junius. We may assert, with pretty strong confidence, 
that Shakespeare wrote the plays which go by his name, 
although many stoutly deny it. But who doubts his own 
existence, or the erection of the Egyptian pyramids, or that 
eagles can fly ? The truth, therefore, of caused truth, is as 
true as any truth. Our uncertainty of it does not affect it. 



REASONING ON NECESSARY TRUTH. 21 

It may affect us ; but to doubt that which is sufficiently- 
proved is utterly unreasonable. 

KEASONING ON NECESSAKY TKUTH. 

In reasoning on necessary truth, we begin with axioms, 
whose truth we see by direct inspection. This direct per- 
ception is alsa called intuition, and is a power with which 
the human mind is endowed to perceive certain truths, not 
merely as true to the extent of its experience or observation, 
but as true in all time and in all space. As examples, we 
have such axioms as, that the whole is greater than any 
part ; things equal to the same thing are equal to each 
other. Such truths the mind perceives to be true on its 
first occasion of experience, as universal truths; yet all 
such truths must show themselves true in every case of 
experience or observation. They cannot, as some say, over- 
ride our experience ; but they must vindicate themselves in 
all experience. Every case must be an illustration of their 
truth. This is what is meant by their being universal 
truths. Of course, if they are necessary, they must be 
universal. 

Beginning, then, with these axioms, or self-evident truths, 
we proceed by logical steps, all of which are easily reducible 
to the form of the syllogism, to reach other necessary truths, 
which are no less true than the first, but whose truth is not 
equally obvious at first sight. We say that multiplying by 
five hundredths is the same as dividing by twenty. We 
may not perceive this at once, but we can easily discover 
that they are in effect the same. It may not be obvious at 
once, that if I have a table eight feet long and four feet 
wide, it contains thirty-two square feet ; but by examina- 
tion, I can see that there must be four rows of eight square 
feet, and thus thirty-two square feet in all. From that in- 
stance, I know that the same is true of every surface. In 



22 EVERY-DAY REASONING. 

all such cases, we proceed from that which is seen to be 
true by intuition to that which is seen, by this process of 
reasoning, to be just as certain as the first conceded truths. 
This kind of reasoning is aptly called demonstrative; and 
the whole process a demonstration. It carries with it the 
highest degree of certainty. 

SEASONING ON CAUSED TEUTH. 

When we come to reason on caused truth, we are not able 
to proceed by such easy steps, since we have no self-evident 
truths with which to start out. We must begin with prop- 
ositions, whose truth is itself a subject of inquiry. As we 
have said, necessary truth, being independent of all volition, 
and having but one way in which it can be, this may be 
learned beforehand, as that all right angles are equal; 
Caused truth, however, was made true by the. adoption by 
some will of one out of the, perhaps, infinite variety of 
possibilities, and, therefore, it cannot be known beforehand. 
It can be learned only by experience. You cannot tell be- 
forehand how many acres a farmer will sow in wheat. You 
can tell just how many degrees there will be in any circle 
he may draw. You know with certainty that, however 
many fields he may divide his farm into, the sum of all 
.the fields will be equal to the whole farm, These latter 
are illustrations of necessary truth. In caused truth, no 
such self-evident truths furnish a starting-point. We see 
that the sheep and cow both chew the cud, and both have 
cloven feet ; but we cannot thence say that all cloven-footed 
animals chew the cud, as we could in regard to the sum of 
the farmer's fields being equal to the whole farm. We can 
see no necessity for cloven-footed animals chewing the cud. 
Indeed, if we look further, we find that the hog, although 
cloven-footed, does not chew the cud. It is thus evident 
that observation is our only resource, and that it is a work 
requiring very great care and caution. To no error are 



CLASSIFICATION. 23 

inexperienced persons more liable, than this of leaping at 
unfounded conclusions. With such false premises, it would 
be strange if our reasoning did not lead us to false conclu- 
sions. That it does so lead, is evident from the blunders 
men are constantly making. It will not do, however, in 
recoiling from such mistakes, to adopt the equally un- 
founded conclusion that all reasoning is hopeless. It is a 
well-established fact that qualities are found in clusters, so 
that one is a sign of the others. It is on this basis that we 
proceed in classification. 

CLASSIFICATION. 

By classification is meant the division of objects into 
groups which are more or less alike. No two things are ex- 
actly alike in every particular; but while there are suffi- 
cient differences to distinguish even the most similar, yet 
there are also very great resemblances. It seems to be a 
natural operation of mind to simplify its labors by omitting 
all particulars not important to its immediate aims, and so 
Hold more firmly those that are of this present importance. 
These last become more obvious by being kept solely in 
view. Of the things thus under consideration, there are 
those which may be considered as a unit, in that they all 
agree in some one particular. The others agree in the ab- 
sence of this one particular. This i3 the simplest form of 
classification, where all the things considered are divided 
into these two classes, namely, those which have, and those 
which have not, a given quality. 

Observation of nature, however, shows that it is possible 
to carry this operation much further, because things are 
found which agree not merely in one quality, but in many 
others also. Thus, the distinction between animal and vege- 
table life is one that includes a great many points of differ- 
ence. So eagles and robins, although both birds, differ in a 
great many other respects beside the beak and the claws. 



24 EVERY-DAY REASONING. 

The camel differs from all other animals used by man for 
travel or burden in a great many points, in which they are 
all alike among themselves. We thus find that there are 
groupings extant in the things themselves. Men may make 
divisions and classifications regardless of these natural clus- 
ters, but such are justly called arbitrary classifications. 
When we follow the groupings of nature, our classification 
is scientific. Perhaps nothing could more certainly mani- 
fest the deep conviction of the human mind that there are 
these groupings of nature, than the readiness with which we 
appreciate the ludicrousness of a fanciful classification. In 
" Gulliver's Travels," we are treated to a description of a 
race of Liliputians, who were divided into two fierce parties 
over the question whether, when an egg was eaten, it should 
be broken at the big end or -the little end. Both the Big- 
endians and the Little-endians asserted that there was a dif- 
ference in the flavor and fitness in this practice. If, now, 
nature has no classifications, and the distinction between a 
bird and a fish has no more meaning and reality in nature 
than this given by Swift, then there can be nothing absurd 
in Gulliver's histories. The truth is, men make only arbi- 
trary classifications. In so far as their classifications are 
scientific, they are only reading the classifications God has 
made in nature. When we are able to read the constitution 
of the world aright, we find all things already in their own 
place, classified ready to our hand. It is here, just as it is 
in a book. The book may be written in a language we can- 
not understand. It contains the thoughts of its author, but 
they are as yet concealed from us. When we are able to 
read the language, we receive and think again the author's 
thoughts. The task for man is, to learn to read aright the 
truths of nature. When we are able to do this, we think 
again the thoughts of God, and that is the perfection of 
science. The task we have in hand is to understand the 
correct methods for this study of nature. 



CUMULATIVE REASONING. 25 

CUMULATIVE KEASOFEM. 

We have seen that, in reasoning on necessary truth, we 
begin with self-evident or intuitive truths, and thence pro- 
ceed by demonstrative reasoning to reach other truths just 
as necessary, but not, at first sight, so obvious. How, now, 
are we to attain certainty in regard to caused truth ? When 
can we know that we read aright nature's classifications, and 
correctly understand her laws ? This is done by an accumu- 
lation of facts and observations which, though at times of 
seemingly small importance at first, may yet, by enlarged 
experience, so increase in number and clearness as to pro- 
duce the most absolute certainty. At other times, the mean- 
ing of the facts is so obvious at once, that we have no doubt, 
and all subsequent experience only serves to confirm these 
our first conclusions. When Copernicus first suggested that 
the earth revolved around the sun, it was a mere hypothesis, 
which everybody's eyes seemed to contradict ; but it is now 
proved by so many facts, that it cannot be doubted by any 
one acquainted with the evidence. 

One single fact makes the truth so indicated possible. 
Some things are possible ; others are impossible. For the 
same thing to be in two places at the same time, is impos- 
sible. It is possible for a man to live a day without food. 
We are certain that fish can swim. At present, it seems im- 
possible for man to live without air ; but if one man should 
do so, that one case would prove its possibility. Added in- 
stances would each increase the testimony in its favor. One 
message by the ocean cable proved such a telegraph possible. 
Whether it would work long and well enough to pay, needed 
other facts, to prove it. That point is now settled also. Be- 
tween, therefore, the mere possibility proved by one fact, 
and the positive certainty which is reached by a sufficient 
nymber of facts, there is every shade and gradation of proof. 
A sufficient accumulation of facts and observations all point- 
3 ♦ 



26 EVERY-DAY REASONING* 

ing in the one direction, will ultimately bring certainty on 
any question. A feather will not balance a pound, but the 
fact that the feather weighs something, proves that if enough 
of them are gathered they will weigh a pound. One feather 
will balance part of the pound, and two feathers will bal- 
ance more, and if enough are accumulated, they are sure at 
length to lift the other end of the scales j and if this pro- 
cess is continued, you can pin the feather end to the floor as 
firmly as by a ton of lead* The term Cumulative Reason*" 
ing, or evidence, rests on the same principle of increasing 
weight, until all doubt may be overcome, and we rest in 
certainty. 

It may be proper here to give the leading points of differ- 
ence between Demonstrative Reasoning, as applied to neces- 
sary truth, and Cumulative Reasoning, as applied to caused 
truth. 

1. The fundamental difference, of course, is that, in reason- 
ing in regard to necessary truth, you start with axioms and 
things self-evident ; while in the other, you are dependent in 
whole or in part on experience. In the first, therefore, no 
experience is needed, and each item of experience is of uni- 
versal application. There is no limit to the progress that 
might be made ; and, if the argument is correct, the conclu- 
sion is certain without trial. In the other, however, we 
begin with trials, and we must test every step which we 
take by repeated trials. However logical the argument, it 
is to be tested as if we were to begin anew just at that point 
of progress. This insisting on constant and unvarying 
experimentation was perhaps Bacon's greatest service to 
science. 

2. In demonstrative reasoning, there is not ordinarily any 
conflicting evidence. All the evidence is on one side. In 
cumulative reasoning, however, there is very generally a 
balancing of arguments, that seem to* contradict each other. 
No argument was ever yet produced to make it appear pos- 



CUMULATIVE REASONING. 27 

sible that two straight lines could enclose a space, or that 
two and ten were anything else than twelve. But how 
many arguments appear on each side of the question, as 
to the habitability of the heavenly bodies. The debates 
of scholars and statesmen are but the marshalling of these 
antagonistic arguments on the various questions in contro- 
versy. In the way of practical genius, nothing is of greater 
value than that power of determining correctly among these 
warring probabilities. This is the true secret of business tact 
and public leadership. 

3. In view of these two, the third difference is obvious, 
namely, that while cumulative evidence admits of degrees, 
demonstrative evidence does not. This last is certain, one 
way or the other. If a proposition is legitimately demon- 
strated, nothing can make it more certain. Every conclu- 
sion reached by it is equally true. It is quite otherwise in 
cumulative reasoning. Here, indeed, we may, and often do, 
rise to absolute certainty ; but in the majority of cases there 
are doubts. The rise in the price of grain next year may be 
very probable, and all through tke passing season the like- 
lihood of this may be increasing, until no thoughtful man 
would sell his crop at a low figure. After all, however, it 
may be a mistake. The perplexity lies in this uncertainty, 
and this leads to the next distinction. 

4. Responsibility is connected with the one, and is not 
with the other. No praise is due to him who believes that 
things equal to the same thing are equal to each other. No 
man can avoid believing that two and two are four. In 
cumulative evidence, however, a man may or may not listen 
to it. Men often do shut their eyes to the plainest proofs, 
and the follies they then commit are sins. It is a duty bind- 
ing on all to consider these proofs well, and, in this light, 
adopt the part of wisdom. Men may demand the irresist- 
ible force of demonstration on all subjects, but it will not 
be given, and cannot be gained in any field to which it 



28 EVERY-DAY REASONING. 

does not belong. It belongs to necessary truth, and not 
to caused ; and those who object to action in the depart- 
ment of caused truth, because they cannot get the kind of 
proof obtainable in regard to necessary truth, are as silly 
and wicked as those who 'would refuse medicines to cure 
malarial disease, because they could not, by a mathematical 
computation, figure out, from the character of the disease, 
the weight of the dose. In its sphere, cumulative reason- 
ing is all we have or can have, and on all the practical 
questions of life it is sufficient for our wants. 



PART SECOND. 
CAUSES. 

°oXKoo 

NATURE'S OPFEKIM. 

TN the world around us, we find a multitude of things in- 
J- viting our inspection. The most casual glance will show 
us that these things are constantly acting and reacting on 
each other. The same thing is, at the same time, both act- 
ing on other things and being acted on by them. We have 
thus two things furnished for our investigation, — the things 
themselves, and their mutual action and interaction on each 
other. There is much discussion as to whether we know 
anything about objects except their qualities. Without in- 
dulging in metaphysical speculation, it will perhaps lead 
us, with more clearness and ease in our present progress, to 
define a quality as any power a thing has to produce an 
effect. Thus, we say sugar is sweet, because, when we put it 
to our tongue, it produces a certain taste there. We say 
vinegar is acid, because, when soda is put into it, certain 
chemical changes go on. We call powder explosive, since, 
when fire is applied, it is suddenly converted into an elastic 
gas. So minerals are heavy, when they press strongly 
towards the earth. Animals are fleet, when they can move 
rapidly. When, then, we are inquiring into the qualities of 
things, we are asking what effects they are able to produce, 
either on our senses or on each other. Color is an effect on 
our sense of sight. Hardness is power to resist pressure. 
We know but little of electricity, except by what it can do. 
In the last analysis, the same is probably true of other things. 
3* 29 



30 EVEIiY-DAY REASONING. 

Let it not be supposed that by this the limits of our 
knowledge are contracted. If we properly enlarge our no- 
tions of cause and effect, we will find that what we have just 
said is only another way of stating what everybody believes. 
The convenience of this statement here is, that it makes it 
our first business in inductive logic to learn how to eliminate 
and identify causes. After that is done, we will be better 
prepared for the more difficult subject of classification. 
Usually, this last subject is put first, and its natural difficulty 
is increased by the want of preparation to understand the 
basis on which the classification proceeds. If we classify 
objects according to the effects they are able to produce, our 
path is plain. We will first find out what effects are at- 
tributable to each object, or what its power is as a cause, 
and then we will know where to place it. Those that pro- 
duce the same effects will be in the same class. We thus in- 
quire into causes, in order to classify the agents. We in- 
vestigate one thing nature gives, the interaction of things; 
in order to find out in what groups she has placed her other 
offering, the things themselves. 

This leads directly to the first great questions of science 
in the department of Caused Truth — WHAT, HOW, and 
WHY. The What inquires for the facts. The How in- 
quires into causes and laws. The Why inquires into the 
end sought to be attained, which is sometimes called final 
cause. The first two belong to material things as well as 
immaterial ; but the last requires an intellectual answer, and 
a reply to it is only possible when we are considering that 
which is the work of mind, and done with a purpose. This 
point will come up again. 

HATUEE'S LAWS. 

The simplest definition of a law of nature, perhaps, is 
this : Such a statement of our past observations, in relation 



nature's laws. 31 

to a given matter, as we believe will be found to hold good 
in all future experience. If we merely tell what has oc- 
curred, that is only history ; but when we step beyond that, 
and try to state the law of the events, we mt an that such 
has been the frequency with which the concurrence of certain 
agents has been followed by certain results, that we expect 
those results to follow that concurrence in the future. A 
superstitious man says Friday is an unlucky day ; because he 
thinks he has noticed that the undertakings he has begun 
on that day have failed so often, he may expert such to fail 
in the future. The physician says the thild will not have 
the measles again, because medical men have noticed that 
people usually have that disease but once, and rhe same may 
be expected in this case. Newton's law of gravitation is, 
that the force of gravitation diminishes as the square of the 
distance increases. It always has been so, anc we have not 
a doubt it will be so in the future. The difference, then, is 
plain. When we state the result of our observations, we 
take the first step towards enunciating a law. When we go 
on and assert it as a general truth beyond prese it experience, 
we take the other step. 

In nature, however, there are none of these, which we 
may, for the present, call tentative laws. Viewed as from 
nature's side, laws are merely the methods in which things 
act. In the things there is no choice, but they act according 
to these laws under which they are made. Even mind has 
its laws of thought and emotion. The will has its laws of 
freedom and responsibility, from which no volition of its 
own can set it free. All these laws, therefore, viewed from 
nature's side, are of the same character — absolut ), and always 
operative. Their action is only to be controller by bringing 
other like laws of greater efficiency to counteract their en- 
ergy. Bodies tend to fall to the ground, but we may pre- 
vent this by placing under them a support strojg enough to 
bear their weight. It is a law of mind to think, and we can 



32 EVERY-DAY REASONING. 

only keep out evil thoughts by occupying the mind with 
better thoughts. 

While, however, all nature's laws are thus equal and uni- 
form in their action, we do not, by any means, always know 
what these laws are, or what the action of different agents 
will be. On our side, therefore, there is the greatest differ- 
ence among these laws. The difference depends on the 
varying degrees of our knowledge. Some are mere sugges- 
tions of laws, by the fact that certain things are seen to 
occur together. These, for want of a better name, we call 
empirical laws. • 

Empirical means blindly following observations without 
regard to causes or reasons. As applied to nature's laws, it 
refers to those cases where the relation of cause and effect is 
not considered, and all that is considered is, that certain 
things have frequently occurred together. It especially in- 
cludes those rules where there is nothing but mere concur- 
rence known to be present, and where there is no attempt to 
assign a cause. Thus, all thsse rules for building fences by 
the signs of the moon, and the predictions of the weather 
founded on the character of certain days, and that children 
have whooping-cough but once, are illustrations of empirical 
laws. Their whole basis is observation, more or less frequent. 
In some cases they rise to a very high degree of probability, 
but in other cases they show in themselves that they have 
very little foundation. These last are wholly unreliable, 
and have, perhaps, as many exceptions as fulfilments, while 
the former are fulfilled with very few exceptions. The dis- 
tinguishing feature, therefore, of these empirical laws is, 
their dependence on mere frequency of observation, without 
any known reason for their existence as laws. 

The other class of laws we may denominate established 
laws. These are laws of nature, where we not only know the 
law, but also the reason for it. It is established by the dis- 
covery in nature of the cause by which its fulfilment is 



nature's laws. 33 

r 

secured. We have, therefore, in these, both the facts and their 
philosophy ; so that the law is a general statement, including 
under it a large class of facts. As an illustration, we say it 
is a law of nature that the frost is not so severe in cloudy 
nights as in clear, because the clouds shut in the earth's 
heat and prevent its rapid radiation, just as a man is warmer 
with a large quantity of covering on his bed, than if he had 
none. The law that the frost was most, severe in clear 
nights, was known long before the reason of it was detected. 
At that time it was an empirical law. It became an estab- 
lished law by the detection of its reason. Sc it is an estab- 
lished law that cropping is more exhausting to land than 
pasturing, because the animals drop their manure on the 
field from which they took their food, and so but little of its 
fertility is taken away, while the removal of both the straw 
and the grain will rapidly diminish its productive power. 
A very admirable illustration of an empirical law that has 
passed into the class of established laws, is the fact of the 
periodicity of the moon's eclipses. By mere observation, 
astronomers had found that these eclipses followed each 
other in a regular succession at fixed intervals. By this 
means it was possible to foretell the time of the occurrence 
of these eclipses. As yet, however, no satisfactory explana- 
tion of the eclipse itself was offered, much less any explana- 
tion of the reason of their regular recurrence. When, how- 
ever, the true theory of the motions of the heavenly bodies 
was discovered, and the laws of those motions ascertained, 
it was found that they required just these several eclipses, 
and just in the order laid down in their periodical tables. 
These empirical laws have thus a constant tendency to be- 
come established laws, or else to be disproved. In other 
words, the human mind has a natural curiosity to seek for 
the reason of all that it observes, and thus either establish 
and explain these empirical laws generalized.from its obser- 
vations, or overthrow them altogether. Very many of the 

C 



34 EVERY-DAY REASONING. 

scientific problems of to-day are the solutions of empirical 
laws, such as the inequalities of the tides at different places 
in the same latitude, the averages, of crimes in large com- 
munities in different years, the improvements in animals and 
vegetables by cross-breeding, and such like. The success 
that has attended past efforts to resolve these perplexities, 
gives strong confidence to future labor. 

We have, then, these peculiarities as marks of these two 
kinds of laws. Empirical laws are, first, the result of fre- 
quent observation alone ; second, their reliability is measured 
by the inequality between the number of cases in experience 
in which they have held good, and the number of excep- 
tions ; third, they indicate the existence of causes which pro- 
duce the results that have been observed, but these causes 
and the laws of their action are as yet unknown. . On the 
other hand, established laws are, first, based on satisfactory 
reasons which explain the phenomena ; second, they have an 
objective reality in the present constitution of the universe; 
third, we are enabled by them to predict the future, and that 
future, when it comes and is fully understood, verifies the 
law by still more clearly indicating the connection of cause 
and effect. Ultimately, all empirical laws ought to become 
established laws, so far as they are true, and subverted in 
every other respect. Much as has already been done in this 
direction, a far wider field remains to reward with its wonders 
the investigations of vigorous and careful students. 

EFFICIENCY OP CAUSES. 

The question whether there are efficient causes or not, is 
one on which the mass of men will have little difficulty. 
We all act on that principle. Even those who theoretically 
deny that there is any such thing as causation, and assert 
that all which we call causation is, in reality, only invariable 
sequence, nevertheless act on the presumption that there are 



EFFICIENCY OF CAUSES. 



35 



real, true causes, and are compelled to adopt that phraseol- 
ogy. Without digressing too far, it may be well to notice the 
following reasons for believing to the full in the efficiency 
of causes : 

1. The first source of appeal is to our own consciousness. 
If we cannot believe it, we cannot believe any knowledge 
whatever. Now, there is no knowledge of which I am more 
fully conscious, and more positively certain, than that, when 
I, by my hand, press on the lever A B at A, and the weight 




W rises in the air, my weight is the true cause of its motion. 
When I take away my hand, it falls again. Or you take 
direct hold of the weight, and as you lift, it moves upward. 
Now no amount of argument can convince an ordinary 
mind that your lifting is not the actual cause of its rising. 
You feel the resistance of its weight, and increase your ex- 
ertion, and by and by you overcome its weight, and it rises 
with your hand. You have before you a quantity of powder, 
and on it you let fall a spark of fire. An explosion follows, 
and every time we repeat it the assurance grows more abso- 
lutely certain, if that is possible, that the spark caused the 
explosion. Old and young, Learned and unlearned, at once 
see the connection of cause and effect. In all our efforts to 
produce the results we desire, we endeavor to accomplish 
our ends by putting into operation the causes by which they 
are effected. ' 

2. In entire harmony with this affirmation of our own 



36 EVBBY-DAY REASONING. 



♦ 



consciousness, is the testimony of the general consciousness 
of mankind. The convictions of men, especially the uni- 
versal unrecognized convictions of men, are indicated by 
their language. You ask a man why he believes the price 
of coal will fall, and he replies, because the miners are work- 
ing for lower wages, and more capitalists have gone into the 
business. His answer begins with the word because, or by 
cause of, as setting forth the reason of his views, and then he 
proceeds to state an adequate cause. Another says the price 
of wheat will be high. If you ask him why he thinks so, 
he may say there is war in Europe, and so the waste of 
breadstuffs will be great, thus increasing the demand, while 
the large number of men taken from the fields to enter the 
army will reduce the supply, and therefore the price will be 
high here. That word therefore, meaning for this reason, 
shows that the results he predicts are, in his judgmeut, to 
be caused by the means he has stated. If we observe all 
classes of men, we shall see not only that they thus use 
these significant words (because, when they state the results 
first and the causes- afterwards, and therefore, when they 
state the causes first and the results afterwards), but also 
that the whole structure of their language indicates that 
they reason on that connection of cause and effect. These 
two words, because and therefore, have their equivalents in 
every language of men. People of all tongues, in their 
doubts and controversies, recognize that as having weight 
in the matter which marks a cause. That which does not 
rest on some form of this relation of cause and effect is no- 
where allowed much weight. That this relation of true 
cause to actual effect is the leal secret of the convincing 
power of an argument, and this the correct analysis of the 
reasoning process in the minds of men, may be tested by 
any one who will try it with children, or any miscellaneous 
gathering of people. If he will show the presence of a 
cause, they will show that they appreciate the argument ; 



EFFICIENCY OF CAUSES. 37 

and if they undertake a reply, in their reply they will be 
found to proceed on the same basis. They may be wholly 
ignorant of all the technical terms of both inductive and 
deductive logic ; know nothing of illicit process, undistrib- 
uted middle, or concomitant variations ; yet they will use 
this connection of cause and effect as the force of their 
argument ; and when these methods of inductive logic are 
explained to them, they will recognize them as the true 
statements of their mental operations in regard to caused 
truth; — just as the uneducated see mistakes in grammar, 
and when they have studied the science of grammar, recog- 
nize its rules as the true tests by which they have always 
judged of the correctness or incorrectness of language. In 
the home life of mankind, at their daily occupations, they 
make experiments precisely on the methods to be hereafter 
explained ; and these methods have no meaning to them, 
unless there is real efficiency in causation. To no one thing 
do the languages and actions of men give a more positive 
confirmation than to this assertion of the reality of causes, 
and the dependency of effects on the active agency of these 
causes. 

3. This same truth of the efficiency of causes will become 
next to self-evident by the consideration of the difference be- 
tween two sets of cases. The application of fire to gunpowder 
has not more regularly been followed by an explosion, than 
day has been followed by night ; and yet no sane person be- 
lieves that day is the cause of night, as they believe the fire 
caused the explosion. All the crows we have seen were 
black, and yet we by no means so confidently believe that 
the next crow will not be white, as we believe that the next 
living man, held for an hour under water, will be dead^ even 
though we never saw a person drowned. Once it was sup- 
posed all swans were white ; but when a species of black 
swans were found, it was not looked on as if we should see 
an ox living after the head had been taken away. One 
4 



38 EVERY-DAY REASONING. 

case, in which a barometer was carried up a mountain, was 
enough to determine that the mercury was sustained in the 
barometrical tube by the pressure of the air; since as it 
went up the mountain side, and so left less air above it, 
the column of mercury fell to a still lower point. Many 
people use old horse-shoes to keep away witches, yet who 
believes that a witch would be hindered by a horse-shoe? 
If we ask why our confidence is so strong in one set of cases, 
and so utterly fails in the other, the answer is plain. We 
perceive a cause, and a sufficient cause for the explosion of 
the powder, the death of the man under water, the death of 
the headless ox, and the fall of the mercury as the barom- 
eter is carried up the mountain side. We see no cause what- 
ever for the night in the preceding day, or for the blackness 
of crows, or the w T hiteness of swans, or fear of horse-shoes by 
witches. Every instance that manifests a cause, furnishes 
us with sufficient reason to believe that the rule is universal, 
and that the same effect will always be secured by the same 
set of circumstances. This leads us to the other important 
consideration. 

4. The Positive Philosophy, which denies all efficiency in 
causation, utterly fails to explain the self-evident difference 
between these two classes of cases. Every attempt to ex- 
plain the reasoning process must, of course, account for this 
obvious difference. If we admit force in causation, the dif- 
ficulty is at once removed, and all is plain. If, however, 
we attempt to reduce all to mere uniformity of succession, 
and say that all that is in it is, that always after the stop- 
ping of a man's breath his death happens, there is no explan- 
ation of this difference in the above classes of cases. No 
more accurate Dr able thinker of this school of philosophers 
has appeared than John Stuart Mill; and yet, after consid- 
ering the specific example of the blackness of crows, he as- 
serts that all the instances that have been observed since the 
beginning of the world, in support of the general proposition 



CAUSES DEFINED. 39 

that all crows are black, would not outweigh the testimony 
of one unexceptionable witness that, in some new region of 
the earth, he had caught and examined a gray crow. He 
then changes the form of the question, and proceeds thus : 
u Why is a single instance in some cases sufficient for a 
complete induction, while in Gthers myriads of concurring 
instances, without a smgle exception, known or presumed, 
go such a very little way towards establishing an universal 
proposition? Whoever can answer this question, knows 
more of the philosophy of logic than the wisest of the an- 
cients, and has solved the great problem of induction." 
That la^t sentence is. a frank confession that, on his own 
theories, the difference between the two classes of cases is 
inexplicable. We are, therefore, left no alternative but 
to accept the only other theory, especially when we find 
that accepting it, the whole mystery is gone utterly. 

As a result, therefore, of these conskjerations, we conclude 
that effects in the universe are activelyNmd efficiently pro- 
duced by their several causes. That whicnNis asserted by 
many to be a self-evident £ruth, is thus found toSae not only 
axiomatic, but the conclusion of the most perfect induction, 
supported by the undivided testimony of all instances, that 
every effect must have its cause. And since we are 
not able of our own volition immediately to produce effects, 
but are compelled to produce them mediately, — that is, by 
the means of their causes, — our knowledge of these causes, 
and of their several effects, is the limit of our power. We 
can only increase our power by increased knowledge. In 
the highest sense, therefore, it is true that knowledge is 
power, 

CAUSES DEFINED. 

What, now, is a cause ? Ordinarily, by a cause we mean 
the new and inconstant agency which precipitates the effect. 
But it will not do to limit the word to these, as if the spark 



40 EVERY-DAY REASONING. 

of fire was the whole of the cause of the explosion of the 
powder. The powder was evidently also part of the cause 
of the explosioi^, since without it the spark would have been 
]] armless. So, further, there was needful to produce the re- 
sult some means of keeping the powder together, otherwise 
the spark would have had to travel from grain to grain, 
instead of the fire being communicated from one grain to 
another. All of these are real causes, and none must be 
left out of* view, if there is to be a complete survey of the 
subject. 

Some have introduced the term concauses to designate 
those causes, which seem to play only a passive part in the 
production of the effect. Perhaps a better division would 
be into subordinate and operating causes. The subordinate 
causes are those whose work is merely to give occasion or 
possibility for the operating causes to act. They merely 
furnish the opportunity, but do not act themselves. Thus, 
to have an explosion, the explosives must be held together 
by some vessel. The vessel is a subordinate, not an oper- 
ating cause. Its material is of no importance. To have a 
fire, you must have some means of keeping your combus- 
tible materials together — such as a stove, a stone, or the 
ground ; but all that the stove or the ground has to do is 
the subordinate part of holding the fuel together! These 
are, therefore, causes, but subordinate causes. They are, 
indeed, necessary for the effect, but the material of which 
they are composed is of small account. 

The operating causes are those which contribute efficiently 
to the result. They again may be divided into dormant 
and active. The dormant are those which, when the occa- 
sion comes, take part in the work, but must have the active 
to set them in motion. They produce no results themselves. 
They sleep, as we might say, until they are awakened into 
energetic action by the presence of the active causes. If 
they are let alone, no result comes. Thus the elements of 



CAUSES DEFINED. 41 

life in the seed, as it lies stored away for future sowing, are 
dormant causes. Properly kept, no action is apparent. 
There must be moisture, heat, and light to set them at work, 
when they bring into existence a new plant. 

The active causes are those which set the dormant in mo- 
# tion, and so seem to be the immediate causes. They are, 
therefore, often spoken of as the causes ; as if nothing else 
assisted in producing the effect. The spark is the active 
cause of the explosion of the powder. The sunshine and the 
moisture are the active causes which set the life of the seed 
to taking up substance from the earth and atmosphere, and 
so constructing a tree. The photographer has all three 
classes of causes at work in making his pictures. His stands 
and cases are subordinate causes. His chemicals are his 
dormant causes, and the light and its colors, which he lets 
fall on the prepared plate, are the active causes. 

It is obvious from this that in regard to the subordinate 
causes, there may be very great variety without materially 
affecting the result ; but that to have in any exact sense the 
same effect, there must be the same dormant and active 
causes. The artist must have some apparatus of some kind 
for preparing his negative and holding the pictures he would 
copy ; but it is a mere matter of convenience what its con- 
struction, or color, or material may be. To have, however, 
the same kind of a picture, he must have the same kind of - 
chemicals, and the same kind of light. The distinction be- 
tween photograph, ambrotype, and ferrotype, is dependent 
mainly on differences of dormant causes. The stands, and 
cases, and sunlight, and people, may all be the same ; but 
the results are very different. ' Strictly speaking, the same 
effects are only produced by the self-same causes. For all 
practical ends, however, we may be able to modify this state- 
ment somewhat, in regard to the subordinate causes. But 
we are only able to do this when we have attained a clear 
knowledge of all the causes, and have fixed on the exact 
4* 



42 EVERY-DAY REASONING. 

work of each, so as to know whether it is a subordinate, dor- 
mant, or active cause. 

THE DIFFICULTIES OF' IDENTIFYING CAUSES. 

Since caused truth depends on volition for its existence, 
there can be but two ways of finding out what is the fact. 

First, The author whose will determined the matter may 
tell us ; or, we may wait until the volition has been carried 
into execution, and then see for ourselves. Thus, it is the 
farmer's business to decide how many acres he will sow in 
grain, and he may tell us what his purpose is in regard to 
the matter ; or, wanting this, we may wait until he has done 
his seeding, and then look at his farm. His information 
and our own observation are therefore the only means by 
which we can attain a knowledge of his determinations. 

The course of nature has been determined by the will of 
God. As in the case of the farmer, so here, there are but 
these two ways by which we can learn this course of nature, 
including these relations of cause and effect. Either God 
must reveal it to us, or we must examine for ourselves. 
While God has seen fit to give us a revelation in regard to 
religion, he has not spoken to us on this subject of science, 
for the purpose of relieving us of the labor of discovery. 
Our only method, therefore, for learning this course of na- 
ture, is to look at the facts as we find them, and from these 
facts learn these relations of cause and effect. 

Before we enter on the study of the methods by which 
these laws of nature are attested in the facts which surround 
us, it is important to get a clear conception of the difficul- 
ties in the way of such a discovery of law from facts, which 
these methods are intended to overcome. These difficulties 
are easily reducible to the one general difficulty of the great 
complexity of the action and interaction of causes. But this 
appears in so many forms that distinct statements of it are 






THE DIFFICULTIES OF IDENTIFYING CAUSES. 43 

required, under these various phases. It will, therefore, be 
developed into five difficulties, thus showing it in as many 
different aspects. This will prevent our undervaluing our 
task, and prevent our judging too uncharitably of those who 
make mistakes. 

First Difficulty. — Causes, perhaps, never act singly. In 
almost every case the three classes are all present — subor- 
dinate, dormant, and active. It may, possibly, be too much 
to assert confidently that no one cause ever acted alone ; but 
it is very certain such cases are almost unknown to men. 
Coming thus in droves together, it is difficult to decide what 
part each takes, or to which of the three classes each belongs. 
Oftentimes, too, there are occult causes at work, and so hid- 
den that their very presence escapes observation for a long 
time. Of course, while their existence is not known, their 
effect will not be recognized. It seems now probable that 
there is, throughout the spaces of the universe, a very atten- 
uated ether ; but, if so, it is so inaccessible to observation 
that its presence is only presumed from the existence of ef- 
fects which seem otherwise inexplicable. On the other hand, 
there are cases where the presence of certain causes appears 
indispensable to the production of the effects, and yet nothing 
can be discovered which they do. In obtaining oxygen by 
heat from chlorate of potassa, sand, and black oxide of man- 
ganese, we find it very difficult to tell what the oxide of man- 
ganese does. The chlorate of potassa gives off more or less 
.of its six equivalents of oxygen, but the manganese remains 
unchanged in the retort. It seems to have an influence; but 
what the nature of it is has not yet been ascertained. 

Second Difficulty. — Causes not only cooperate with each 
other, but they also interfere with each other's effects. If 
they were always at work in the same direction, or else in- 
active, the case would be much simpler. Sometimes, how- 
ever, two causes may be actively at work without any visible 
effect, because they just neutralize each other. Two engines, 



44 E VERY-DAY REASONING. 

attached to the same end of a freight car, may draw it easily; 
but if attached to different ends, they may exert their whole 
power, and no motion in either direction result. So in med- 
icine, there are cases where a patient is suffering from a com- 
bination of diseases, in which the remedy that would relieve 
one disease only aggravates the other. While, therefore, both 
diseases assail the health of the patient, the medicines are 
mutually destructive of each other. This interference of 
causes with one another is a very constant perplexity. 

Third Difficulty. — The same general result is produced by 
different causes. Sickness may be the result of the diet the 
people have been eating, or the impure air they have been 
breathing in their unventilated rooms, or malaria arising 
from decaying vegetable matter, or stagnant water, near by. 
Moreover, some forms of fever are more or less contagious, 
and some constitutions have to some extent a hereditary 
tendency to certain fevers. The treatment may require to 
be somewhat varied, as one or the other of these causes has 
been the origin of the disease, yet how difficult to determine 
with certainty to which of these it is due. So national or 
commercial prosperity may be produced by a very great 
variety of circumstances or combination of circumstances. 
The advertising pages of the agricultural papers are a suffi- 
cient proof that there are a great many kinds of fertilizers, 
which will increase the productiveness of the soil. While, 
therefore, in strictness, there must be the same causes to 
produce the same results, yet, to our ordinary observation, 
the same general results may be produced by many different 
causes. 

Fourth Difficulty. — Naturally, we would expect that either 
increase or diminution of a cause would proportionately in- 
crease or diminish the effect. If it did, this would furnish 
a ready way to identify causes and effects in many cases. 
This, However, is by no means the case. In so simple a 
matter as the effect of heat on water, we have a famous 



THE DIFFICULTIES OF IDENTIFYING CAUSES. 45 

illustration of this. If we take water at a temperature of 
Fahrenheit, and increase its heat, it will expand 

until converted into steam ; but if we reduce its temperature, 
it will contract until it reaches about 39° Fahrenheit, when 
it begins to expand as it grows colder, until it reaches the 
freezing-point, when a very considerable expansion takes 
place. This last is of itself somewhat of an anomaly. 
Almost all substances contract in cooling from a fluid to a 
solid state, but here we see water does just the reverse, 
under the same process. With a singular perversity it ex- 
pands both ways from about 39° Fahrenheit, so that the 
effects of the heat are the same, whether it is increased or 
diminished from that point. 

:!th ! . — Things apparently related as cause and 
effect, may both be effects of the same cause. Causes do 
not limit themselves to the production of solitary effects. 
As the causes come in clusters, so the effects may start forth 
in companies. Some may appear immediately, and others, 
being delayed, will have the appearance of effects of these 
antecedent effects. This difficulty is especially serious in 
social science studies. Here the movements which take place 
in communities bring about successive results, and these are 
often mistaken for causes of one another. As causes con- 
verge at the point of efficiency, and effects start divergent 
from the same point, great care is required to avoid the 
wrong location of these causes and effects. 

As has already been stated, all these difficulties are in- 
cluded in the great complexity of the action and interaction 
of causes. T ne 7 come helping, hindering, co-operating, coun- 
ter-acting, aiding, and interfering with each other in such 
diverse, contradictory, and arbitrary ways, that it is not 
strange that, from the beginning, men have blundered and 
been mistaken. But with these difficulties to overcome, we 
have therein only additional incentives to action, and stronger 
motives to a careful study of the methods by which these dif 



46 EVERY-DAY REASONING. 

Acuities may be solved, and these mysteries wrung from the 
seemingly unwilling hand of Nature. While, however, Na- 
ture seems to puzzle us with her complexities, she is lavish 
of her facts, in which these secrets are contained. They are 
strewn all about us in the most profuse abundance, as if to 
tempt us to their study, each offering the most positive assur- 
ance of giving us trjue testimony. It is not equally obvious 
in all cases what this testimony is, and, therefore, not a little 
will depend on our selection for study of those facts whose 
meaning is most clearly presented, 

SELECTION OF FACTS, ■ 

Facts are of two kinds — those furnished by Nature, and 
those produced by ourselves. The first of these are called 
observations, and the others are called experiments. It is 
only in a limited number of departments of Nature that we 
can make experiments. We cannot make a little solar sys- 
tem, and put it to work on our table, as we can mix gases 
and see the result ; nor can we make miniature nations, and 
try their prosperity, now with a tariff, and now with free 
trade. In such matters, we can only take the facts as they 
are furnished to us in Nature and by history, and solve their 
meaning as best we may, In other departments, however, 
we can experiment upon Nature. In such cases, we take 
the facts Nature offers in the regular course of events, and, 
obtaining hints and suggestions there, we rearrange the 
causes, that they may act under new combinations, and by 
this experimentation we, as it were, subject Nature to a 
cross-examination. To this we are rather invited by Na- 
ture, and, make it as rigid as we please, we meet with no 
reluctance to answer. Sometimes it is possible so to shape 
our experiments as to make their result an explicit affirma- 
tion or denial by Nature of some theory proposed for settle- 
ment. When it was asserted by one set of philosophers that 



SELECTION OF FACTS. 47 

the fall of bodies was proportioned to their weight, and that, 
therefore, a ball of lead weighing two pounds would fall 
twice as fast as one weighing one pound, and others said 
that bodies of the same material, no matter what their 
•weight, would fall in the same time, the experiment of 
letting two balls of unequal weights drop from the top of 
the leaning tower of Pisa demonstrated, in the sight of 
every beholder, the truth of the last theory; for both 
struck the ground at the same instant, Such cases of ex- 
periments are the supreme desideratum of every investigator. 
Both kinds of facts are reliable. Neither natural nor ar- 
tificial phenomena are to be discredited. Though we may 
sometimes arrange the circumstances and combinations un- 
der which causes act, no act or volition of ours can in the 
least change their nature or activity, so as to make them 
act differently under a given set of circumstances at one 
time and at another. We can only control or influence 
the action by change of circumstances or combination of 
causes. All facts are equally trustworthy, So we get the 
real, exact facts, it matters little whence they come. Our 
success, however, in reading the laws of Nature set forth 
and exemplified in these facts, will depend very much on 
the ease with which they may be interpreted. Scientific 
induction is observation and experimentation carried on 
under rigid rules, by which we may the more correctly un- 
derstand the relations of cause and effect indicated therein. 
All facts are not equally beset with the difficulties of iden- 
tifying causes, as explained in the preceding section. Some 
general remarks are, therefore, to be made on the manner 
of making these observations and experiments. It is not 
strictly accurate to speak of making an observation. We 
make experiments and we take observations. We cannot 
always arrange Nature for observation ; if we do, that is 
exactly what is meant by making an experiment. When 
we watch Nature in her own operations, under her own 



48 EVERY-DAY REASONING. 

arrangements, we are mere spectators, and so take an obser- 
vation. But as out of all observations taken we may select 
for study those best suited to our purpose, and out of all the 
experiments that could be made we need actually make only 
those furnishing the desired information, in the most intelli- 
gible form, the same rules will guide in both cases. Observ- 
ing these rules, we shall be able to expend our strength in 
the investigation of those facts where there is most likeli- 
hood of our reaching clear and correct conclusions. It is 
not wise to waste time on insoluble mysteries, when we can 
ordinarily furnish ourselves with facts containing the same 
truths, but in a much more intelligible form. 

Rule First — Take those capable of the longest and closest 
inspection. 

Very interesting problems, relating to the sun and moon, 
seem only answerable from observations taken during a total 
eclipse of the sun. These rarely last over a minute or two. 
When, then, one was to occur, visible in Siam for seven min- 
utes or more, the whole scientific world was interested, and 
almost every civilized nation fitted out an expedition with 
the best instruments, and directed by their most learned 
astronomers. In all such cases now, photography is exten- 
sively employed, since it gives the most exact representa- 
tion of the eclipse, and, retaining it, enables the student to 
study it closely after the eclipse is over. One of the great 
difficulties in the study of mental science is to retain the 
same mental state long enough for the careful examination 
of self-consciousness. Mineralogy and natural history owe 
much of their rapid progress, in some directions, to the fact 
that many of their specimens can be placed under the mi- 
croscope, and there watched day after day. 

Rule Second, — Take those with the fewest causes at work, 
and so secure the least complexity attainable. 

In the department of social science this complexity and 
multiplicity of causes is a very serious obstacle. Suppose 



SELECTION OF FACTS. 49 

we are studying pauper legislation, and we find a case where, 
after the passage of certain laws on the subject, pauperism 
was greatly diminished. If now there was nothing else at 
the same time which might affect the subject, our conclusions 
would be quite reliable. But suppose that about the same 
time the financial market became very prosperous and busi- 
ness very profitable, and as a result labor received very 
liberal compensation, it would be easy to mistake the results 
of one set of causes for those of another. As a rule, in these 
social questions there are a great many causes operating, and 
too great importance, therefore, is often attached to results 
that follow certain events, since they may or may not be 
their results. On this account, therefore, the greater care is 
needful in examining each several case to determine how 
much value it has for argument. Sometimes a case can be 
found where only one feature was modified, and where, from 
its surroundings, we can have but little difficulty in per- 
ceiving that this modification alone was all that could have 
brought about the result. Such instances will have a supe- 
rior importance in proportion to their conformity to this rule. 

Ride Third. — Take those where the record is most exact, 
and measure everything that can be measured. 

As a rule, estimates are very unreliable. This is especially 
true if they have been made by those who have not had a 
previous training in exact measurement. In so simple a 
matter as estimating the number of persons in an audience, 
persons who have not had some experience in counting 
audiences will usually guess from two to three times too 
many. Not one person in fifty, who has not had practice, 
can go to the blackboard and mark off on a given line 
twelve inches of space. But on the other hand, experience 
can bring this gift of estimating sizes and numbers by the 
eyes to a wonderful degree of accuracy. A drover can tell 
very nearly exactly how many cattle are in a given field 
without counting them, When, now, our future action de- 
5 D 



50 EVERY-DAY REASONING. 

pends on our knowledge of facts, how very important that 
we should have the exact facts. The most expert may well 
count them. Especially is this true if our figures and 
reports are offered as the basis for others to argue on. We 
owe it to them, to truth, and to ourselves, to give figures, not 
from guess-work, but from measurement. No excuse can 
or ought to be accepted for the neglect of this. Multitudes 
of reports are utterly valueless because they are not accurate ; 
and no man deserves to be allowed to call himself a philoso- 
pher who, in any case, accepts for his data anything less 
than the most reliable statistics.^ Every man w T ho patiently 
and accurately observes any set of phenomena, and faithfully 
records, not his inferences, but what occurs, is truly a bene- 
factor of his race and a promoter of knowledge. 



PART THIRD. 
METHODS OF INDUCTION. 

GENEKAL STATEMENT. 

VARIOUS methods have been suggested as the true state- 
ment of the process of the mind in reading the laws re- 
vealed in the facts so gathered* The work that made Bacon 
immortal was his effort to state, in the formality of words, 
these mental operations by which we reach our reliable con- 
clusions. Though highly respectable as a scholar, his at- 
tainments in that direction have been fkr outstripped by 
many now unknown to fame. His great claim to human 
gratitude is in this, that he was the first to urge the supreme 
importance of testing theories by facts, and to insist on the 
abandonment of every theory, however plausible, which was 
contradicted by the facts. His aphorisms were designed by 
him as a kind of proverbial philosophy by which investiga- 
tion should be directed. Many of them are of little account, 
but his phrase, " The proper rejections and exclusions" and 
his explanations and illustrations of instances and examples, 
were so apt a statement of the mental operations, that they 
at once passed into the popular thought of scientific men. 
Indeed, the single phrase above quoted is incontestable proof 
that, however indistinct some of his utterances were, he really 
•saw the true method of inductive reasoning. What he 
meant by making the proper rejections and exclusions was 
that, by selecting test instances and examples, the various 

51 



62 everY-day eeasonxkg. 

false theories proposed for the solution of a given set of facts 
should be one by one rejected because the experiment or 
fact under consideration excluded the possibility of its being 
true. His "Prerogative Instances" were cases which, 
between two rival theories, decisively denied the one and 
affirmed the other. His " Experimentum Crucis " was a 
case which verified one theory and exploded every other* 
His book is very Well worth the study of every one wishing 
to make himself familiar with the subject. Perhaps the 
next most important attempt to formulate these methods in 
words was that of Whewell, in his work on " The Philosophy 
of the Inductive Sciences." The same author published 
another work on " The History of the Inductive Sciences," 
which is one of the most famous works of his or any age. 
His effort to explain the philosophy of these studies was by 
no means so successful as his history. He recommended a 
system of lines representing the facts collected, that thus 
by the eye an estimate might be made of results and the 
uniformities detected. He laid great stress on " Clear and 
Appropriate Conceptions/' and gives many useful rules for 
their attainment, but these rules have not proved themselves 
especially practical. He also attempted a classification of 
methods, naming them the method of curves, the method of 
means, the method of least squares, and the method of residues. 
Through all of his discussion of these there are most valu- 
able hints, and, as in Bacon's, so in his, there are very many 
suggestions and rules which are directly in the line of true 
inductive logic. While not able to complete the science 
of inductive reasoning, these two made large additions to 
human knowledge in that direction, and greatly prepared 
the way for all who come after them. Sir John Frederick 
William Herschel published a work on "The Study of 
Natural Philosophy," which is of the very first order of 
merit, and is counted a standard by all modern writers on 
the subject. It is peculiarly apt in its selection of and com- 



THE METHOD OF AGREEMENT. 53 

ments on its examples of inductive reasoning. Probably 
the greatest recent work is John Stuart Mill's " Logic." His 
names of the methods have now been all but universally 
adopted. They carry their own recommendation in the apt- 
ness with which they express the various processes to which 
they refer. Although wholly in error as to his notion of 
what a cause is, yet Mr. Mill uses the word in its proper 
way, and so, as not unfrequently happens, a word is used 
correctly and explained wrongly. Mr. Mill reduces causa- 
tion to mere uniform succession, and thus, with the whole 
positivist school of philosophers, of which he is one, denies 
all efficiency in causes. This theory has been sufficiently 
refuted in a previous section. Mr. Mill gives five different 
canons or rules, with as many names, but as his third is only 
a combination of the first and second, and it is to be pre- 
sumed that every person of sufficient thoughtfulness to use 
any of these methods intelligently, will use all of them, in 
every case where they are available, there seems to be no 
need of making their combinations distinct methods. We 
shall therefore proceed to the statement 0/ the four methods, 
under the names given by him, to wit : The Method of 
Agreement, The Method of Difference, The Method 
of Residues, and The Method of Concomitant Varia- 
tions. 

THE METHOD OP AGKEEMENT. 

All the cases of the existence of a given effect, 
however they may otherwise differ or be varied, 
will agree in the presence of its cause or causes. 

This is the statement of the rule, when we are reasoning 
from effects and are seeking for their causes ; but oftentimes 
we are compelled to reason the other way, from cause to 
effect. Indeed, in every case where it is possible, especially 
where our reasoning from effect to cause has led us to a # 
conclusion not absolutely certain, we should adopt this 
5* 



54 EVERY-DAY REASONING. 

reverse method, as a test. If we are right as to our hypo- 
thetical cause,* its effect will be produced w r hen it is set in 
operation. But the rule needs some modification to adapt 
it to this way of applying it, and may be stated as follows : 

All cases of the existence of the cause, however 
otherwise they may differ or be varied, will agree 
in the manifestation of its effect, unless there is 
present some adequate counteracting cause. 

When the effect has been produced, and we are looking 
for the cause, we know there has been no counteracting 
cause. But when we set causes at work, our experiment 
may fail, owing to the action of some interfering agent; 
and if we at once conclude that, therefore, this was not its 
true cause, we would drop into great error. Oftentimes the 
discovery of that hostile agent is as important as the rela- 
tion of cause and effect, and thus, while it increases the in- 
tricacy of our problem, it also adds value and interest to 
our researches. As a truth variously stated is thereby made 
clearer, there is added another statement, which is in sub- 
stance the same as the last. Whatever antecedent can be 
excluded, or absent without prejudice to the effect, is no part of 
the cause. 

Beyond the statement of these rules, perhaps no further 
proof of their truth is possible than what is found in illus- 
trations of them. Their illustrations, in addition to this 
use of explaining the rule, will have this advantage, of 
being samples of the method of their employment, and of 
reasoning under them. Suppose we are investigating the 

* In the statement of the rule the word cause was given both in the 
singular and in the plural (cause or causes), to indicate that there 
might be, as indeed there usually is, a concurrence of causes necessary 
to the effect. Hereafter, however, the word will be used in the sin- 
gular only, as including all that is needful to produce the effect, both 
in the way of actual forces and of their relation to each other. The 
word cause will, therefore, mean the combination needful to the effect. 



THE METHOD OF AGREEMENT. 55 

nature of rust. We begin by looking at all the kinds of rust 
with which we are familiar, and examining vherein they 
agree. A little inspection \vill show that it is not on wood, 
but on metals. Further inquiry may bring to our knowl- 
edge other metals that will rust, of which we were not at 
firslb aware. We now notice what the circumstances are ■ 
wherein this rust comes on these metals. We find it comes 
on them both in the air and the water, but mo.'e rapidly in 
water. Our next step is to look wherein air and water 
agree, and we find that while air is oxygen end nitrogen, 
water is oxygen , and hydrogen, thus agreeing in the pres- 
ence of oxygen. This naturally suggests that the union of 
the metals with the oxygen may be the cause of the rust. 
If now the rust is analysed, it is found to be composed of 
oxygen and the metal. From these agreements we con- 
clude that rusting is the oxidization of metals. 

Suppose we are investigating a case of suspeci ed poisoning 
by arsenic, we will proceed by the same method. We know • 
what results will follow when arsenic is treated in different 
ways. If the sulphuret is mingled with finely powdered 
charcoal, and placed in a small tube of hard glass, and the 
end that contains the mixture is heated red hot, the arsenic 
will be sublimed in a small black band or mirror a little 
higher up the glass tube. So if a suspected substance is 
mixed in a retort, with zinc and dilute sulphuric acid, and 
the gas generated is made to escape through a burner, it 
will, when lighted, deposit a bright black spot on a piece of 
cold porcelain held over it. So if the substance supposed 
to contain arsenic is diluted with water enough to make it 
thin, and hydrochloric acid added to the extent of one- 
eighth of the amount of the mixture, and the whole heated 
to near the boiling-point, when a piece of bright copper is 
dipped in it, there will be deposited on it a thin steel-gray* 
coating of metallic arsenic, which, with furthe: 1 treatment, 
can be positively distinguished from all other matters that 



56 EVERY- DAY REASONING. 

are similar in appearance. It is asserted that if arsenic is 
present to the extent of one part in 250,000 of the solution, 
it will show itself by this last test. If now all these results, 
known as following the presence of arsenic, should show 
themselves in a case of supposed poisoning, there would be 
no hesitancy in declaring that arsenic had done the work ; 
and that argument would be wholly on the Method of 
Agreement. 

If we inquire what crystallization is, we find the cases in 
which it takes place agree in that a solid is deposited from 
a liquid state. The prevalence of the cholera in this coun- 
try has shown this in a marked degree, that intemperance 
is very destructive to the vitality of certain parts of the hu- 
man system, inasmuch as scarcely any intemperate persons 
who were attacked with it recovered. The deaths among 
the drunken who took it were a very much larger percent- 
age than they were among those of strictly temperance hab- 
its. It is believed that yellow fever is largely attributable 
to filth, since its presence is mainly confined to cities where 
there are inefficient sanitary regulations. If a housewife in- 
quires what it is that separates the butter from the milk, she 
will see that, notwithstanding the various shapes, and sizes, 
and kinds of churns, they all agree in this: that they are 
methods of agitating the milk, and she will correctly con- 
clude that this agitation is the essential point. It is a strong 
argument for education that, in all the history of the world, 
no enlightened people have been for any long time enslaved. 
It is equally true, and equally instructive, that no republi- 
can government has long endured among a corrupt people. 
These illustrations of truths, proved by the agreement of the 
facts of all experience, might be multiplied almost iadefi- 
nitely. 

* Each of these methods has some feature wherein its use 
is peculiar. In this way certain rules become important. 
Thus in experimenting under this Method of Agreement, we 
are to follow this 



THE METHOD OF AGREEMENT. 57 

Special Rule. 

Vary every circumstance as ranch as possible, except the hy~ 
pothetical cause. 

The conclusiveness of our experiments or observations will 
"be greatly increased if the cases show a difference in every 
particular but the hypothetical cause. It is not possible to 
attain this in all cases ; but so far as it can be done, it is 
desirable. Sometimes it will be found that there are several 
things, in any one of which a variation will affect the re- 
sult. This will facilitate the analysis of the combination 
of causes by which the result is produced. The fact of a 
combination of causes will be clearly indicated if there are 
found several things, the absence of any one of which will 
defeat the result. Some writers, in order to include this 
condition of affairs, use this phraseology — that the thing 
in which the cases agree is either the cause or part of the 
cause. 

In investigating subjects w r here experimentation is impos* 
sible, the observations taken under as diverse circumstances 
as possible, and where the agents were as varied as possible, 
will be the most valuable at first ; but in no case should any 
facts within our reach be neglected. Every case should be 
examined. If its conditions are very similar to those al- 
ready reviewed, its testimony will be valuable for confirma- 
tion. If its conditions are new and peculiar, its testimony 
will be so much the more important. The only time when 
additional cases may be neglected, is when the fewness of 
the causes, and the simplicity and uniformity of their ac- 
tion, leave no doubt that additional facts of the same kind 
could furnish no new light, and where we have applied all 
the tests of inductions, which are given in the section on 
that subject. 

This method labors under this defect — that it is always 
exposed to error from the presence of occult causes not im- 
mediately obvious. The multiplicity of causes also makes 



58 EVERY-DAY REASONING. 

it a rare case that observations shall not have quite a number 
of points of agreement which are of no importance. To ob- 
viate these uncertainties of this method, we have recourse 
to the next method. 

TEE METHOD OF DIFFEKENCE. 

The cases where the effect is absent, however 
similar they may be to those where the effect is 
produced, will always differ from them in the 
absence of the cause. 

This is the general principle. It has, however, some ex- 
ceptions. Thus the absence of the effect, as has already 
been noticed under the preceding method, may be due to 
the presence of some adequate counteracting agent. In 
that case, it would not be correct to conclude in accord- 
ance with this rule. So, also, the presence of a cause may 
be accompanied with other manifestations, which are not 
efficient agents, and yet appearing and disappearing with 
the cause, they may be mistaken for the cause, inasmuch 
as they may be more obvious. Great care must, therefore, 
be taken to ascertain whether the hypothetical cause, whose 
presence or absence we are watching, is a true cause or not. 
In order to make this point more obvious, the rule of this 
method is sometimes stated in the following words : If the 
presence of any given effect is removed from any given set of 
circumstances, on the removal of a given cause, or in case of its 
absence, its presence is obtained by the introduction of that 
cause, then that agent is at least part of its cause. 

The general application of these principles is to the active 
causes ; yet the same processes will apply to the determina- 
tion of the character and influence of all the other causes, 
whether they are subordinate or dormant. If they are sub- 
ordinate, then various other things may be substituted, pro- 
vided they are all capable of doing the same subordinate 



THE METHOD OF DIFFERENCE. 59 

work. By this means, it is usually possible exactly to 
measure the nature and importance of these inferior agents. 
Several may be able" to do the work, and yet, from the pe- 
culiar character of the work, they may not do it equally 
well. It is a great matter to be able to determine what 
subordinate agent is best suited, even for subordinate ser- 
vice. If the causes are dormant, changes cannot be made 
and the result be the same in all its features. The same- 
ness of the result will depend on the end we have in view, 
or at least this is the ordinary estimate of the human mind, 
and the common use of language. Looked at from one 
point of view, and considering some ends, very different 
effects are called the same ; and although called the same 
in that sense looked at, with another thought before us we 
call them very different. In strictness, no result ought to 
be identified with another similar one, unless the dormant 
as well as the active causes are the same ; and their same- 
ness will be admirably tested by this method of difference. 

Suppose a farmer is inquiring foi* the reason of the failure 
of certain of his fields to produce . good crops. He will 
begin to study them by the Method of Difference. He will 
compare them with fields nearly similar in the same neigh- 
borhood, which, notwithstanding the similarity, are very 
productive. He may see that in the other cases there are 
streams of water, which always keep them damp in the pro- 
tracted dry seasons, while his own fields are without such 
moisture. He may thence conclude that the soil is not well 
adapted to retain moisture, and if so, there are two ways of 
further investigation. He may by cutting new drains or 
water-courses be able to irrigate part of his poor field, and 
leaving the rest without irrigation, he experiments on his 
own land. Should the result be that the watered land has 
its productiveness greatly increased, his course is to bring 
water to all such fields, if possible. But suppose this should 
fail, and the watered land be no better than the other, he 



60 EVERY-DAY REASONING. 

will be disposed to try fertilizers, on the supposition that 
certain valuable elements are wanting in the soil. Unless, 
now, he has some previous observation to give him a hint 
that a particular element is probably the one that is want- 
ing, he will naturally try several on different parts of the 
same field. We will suppose that on one part he puts lime, 
on another phosphates, and on another ammoniated man- 
ures ; and when the harvest comes, the part on which the 
phosphates were spread is by -far the most productive, the 
result will be a very plain indication that these phosphates 
furnish the needed elements of fertility. In such experi- 
ments on the farm, it is important that the various fertil- 
izers should be used the same season, otherwise it is very 
possible that the very great differences observed may be 
due to other causes. Many neighboring farmers come to 
directly opposite conclusions concerning the same manures, 
because all try them in different seasons ; and so the results 
are mixed up with the effects of the weather, and numerous 
other causes affecting ve^tation. 

The department of chemistry affords the most beautiful 
experiments, illustrating this process of reasoning by the 
Method of Difference. If a vessel is filled with a solution 
of acetate of lead, and into this solution two thin platinum 
wires are inserted, and these are connected with a small 
voltaic battery, and then the voltaic current is sent through 
the solution, the lead will be slowly severed from the atoms 
with which it is combined, and begin to crystallize on one 
of the poles of the battery, taking forms of magnificent 
beauty. When seen, they will look like vegetable growths, 
springing up so rapidly that their fern-like forms seem to 
grow before the eye. If now the current is reversed, these 
fronds will at once begin to dissolve on the pole where they 
were growing, and in a little they will begin to grow on the 
other pole. Reverse the current again, and again they com- 
mence growing as at first, and dissolving where they grew 



THE METHOD OF DIFFERENCE. 61 

before. It is completely proved that this crystallization is 
due to the voltaic current separating the elements ; for the 
change of the course of the current is the only difference in 
the two cases. 

Suppose the subject for inquiry is as to the element in 
the air by which combustion is supported. The air is com- 
posed of three parts of nitrogen and one of oxygen, mechan- 
ically and not chemically united. If, then, it is the nitrogen 
that maintains combustion, and that nitrogen is obtained 
pure, and so separated from the oxygen, a taper ought to 
burn in it w T ith as great or greater brilliancy. When this 
is tried, the lighted taper is immediately extinguished. By 
the Method of Difference* therefore, it is shown that nitrogen 
is hostile to combustion, instead of a supporter of it. When 
now the same method is tried with pure oxygen, everything 
that is dipped into it burns with very greatly increased 
rapidity. A candle, vrhen blown out, will be at once re- 
lighted when it is inserted in oxygen, if the least spark of 
fire is still found in the wick. A red-hot iron inserted 
will burn with the most brilliant* sparks. When taken out the 
burning at once ceases, to be resumed again if it is replaced. 
A steel watch-spring, when heated red hot and inserted in 
oxygen, is one of the most magnificent experiments that can 
be made. Here the proof is positive that the oxygen is, and 
the nitrogen is not, the supporter of combustion. 

Before further illustration, it may be well here to intro- 
duce some remarks on the application of this Method of 
Difference. As its nature is just the reverse of the Method 
of Agreement, its special rule is exactly the reverse, and is 
as follows : 

Maintain every circumstance as nearly the same as possible, 
except the presence or absence of the hypothetical cause. 

If many variations are allowed, the difference of result 
may be due to these variations, and not to the supposed 
cause. Herein lies the difficulty of the application of this, 
6 



62 EVERY-DAY REASONING. 

method to natural phenomena, where we can only take ob- 
servations and cannot make experiments. The variations 
are numerous, and often great, and so no one case is suf- 
ficient to prove or disprove any but one fact, and there are 
many involved. Where we can for ourselves arrange our 
experiments to suit our own objects, we can vary but one 
thing, and so secure a definite result. This is the impor- 
tance that attaches to conducting agricultural experiments 
on the same season instead of different seasons. When ex- 
periments tried in different seasons are compared, there is so 
much due to difference in temperature, and the order of the 
succession of the extremes of heat and cold, and the differ- 
ences of moisture, and such like causes, that often the results 
are of no value whatever. So in social science -studies, cer- 
tain laws are passed on specified subjects, and a given result 
follows. But at the same time, other laws were passed, 
other financial changes took place, new machines were in- 
vented, and the whole change may be due to these last. 
Indeed, very notable results are oftentimes due to sudden and 
almost unaccountable currents of popular sentiment and 
public prejudice. If, then, these are attributed to legislation 
or finance, we shall fall into great error. 

To illustrate this point, as well as the general subject fur- 
ther, suppose a physician is attending a patient, whose dis- 
ease has not yet developed itself sufficiently to indicate its 
exact character. He has found one remedy prove of no 
avail, and wishes to try the effect of another. At the 
same time that he prescribes the new remedy, he also 
changes the diet and the regulations for ventilation, with 
a different temperature of the sick chamber, and prohibits 
all conversation, and enjoins as much sleep as possible. 
It is evident that the good results which follow can with no 
confidence be attributed to the new remedy. The failure 
of the previous remedies may have been wholly due to bad 
nursing, and the very favorable results now manifested may 



THE METHOD OF DIFFERENCE. 63 

be the beneficial effects of these previous remedies, when by 
oetter nursing their effect and operation was not impeded. 
It may be wise medical practice to change many of the 
remedial measures at once ; but if the sole object in view is 
to test the effect of any one agent, the experiment must be 
made by introducing or withdrawing it alone, without any 
other changes. 

One of the strongest arguments to prove that Sir Philip 
Francis was the author of the Letters of Junius, is of this 
same nature, in that, as soon as Sir Philip Francis was sent 
to India as Governor of India, Junius ceased to write. He 
eould not write political lampoons in England when he was 
ruling in India. By this same means, the character of crim- 
inals is detected. Suddenly a well-known vicious character 
appears in the city, and at once a certain class of depreda- 
tions begins to be reported. In a short time the police learn 
that he has left the city, and immediately these depredations 
eease. Now, although no eye has seen him in his robbery, 
and no evidence available for his arrest is to be obtained, 
yet if this feature marks his frequent visits to that and other 
cities, no man will doubt that he is the guilty party. The 
iron worker finds his fire injuring his metal, and so begins 
to investigate the composition of his coal, and discovers sul- 
phur in it Thinking that this sulphur may be the cause of 
the annoyance, he first burns or chars the coal, so driving 
off the sulphur by heat, and leaving the pure carbon. He 
now finds his iron work free. He then returns to the use of 
the native coal, and the same injurious results follow again. 
He has now identified sulphur as an injurious element in his 
working iron, and so, instead of using the natural coal, he 
puts it through a coke-oven, and thus frees it of these for- 
eign elements. 

The fundamental truth, on which both the Method of 
Agreement and the Method of Difference are based, is this: 

Effects will appear and disappear with ilie appearance and 



64 EVERY-DAY REASONING. 

disappearance of their causes. This will always hold good, 
unless, as has already been suggested, the effectiveness of 
these causes is destroyed by some interfering agent. This 
danger is always to be guarded against when we are reason- 
ing from the presence and absence of causes to their effects ; 
for the absence of the effect, while, of course, it will always 
occur in the absence of the cause, will also occur when that 
cause is present, but overcome by some interference. But 
if we reason from effects, we know that on their appearance 
there is no adequate interference. 

On the general principle stated above, it has seemed to 
some that there ought to be a method, called the joint 
Method of Agreement and Difference. It may, therefore, 
be well to urge here that careful reasoners will not only 
employ the one method that may seem to them best adapted 
to the particular subject in hand, but will strive to use 
every method that may even in a less degree be available. 
The errors of the one will be likely to be detected by an- 
other. The hints suggested by one may be confirmed or 
confuted by another. The Methods of Agreement and 
Difference are peculiarly suited to be used together, and 
probably are more frequently used together than any other 
two ; but when they are thus used together, it is not a new 
method, but the use of two methods, with no new rules and 
all the old ones. Also, not only may these- two be used to- 
gether, but any two may be. used together, as the nature of 
the case will call for; and there have been, and will be, 
cases where all four methods will be used and lend their 
aid. Too much stress cannot, therefore, be laid on the im- 
portance of combining any or ail methods, whenever prac- 
ticable. If we are on the trail of truth, every indication 
will point the same way ; and if we are misled, it is of first 
importance that w r e should abandon the pursuit just as soon 
as the error is shown. By all means, therefore, let us in 
every case resort to all the methods, if they can be applied. 



METHOD OF RESIDUES. 65 

METHOD OP RESIDUES. 

When in any phenomenon we find a result re- 
maining AFTER THE EFFECTS OF ALL KNOWN CAUSES 
ARE ESTIMATED, WE MAY ATTRIBUTE IT TO A RESIDUAL 
AGENT NOT YET RECKONED. # 

The difficulty of this method is such that two other state- 
ments of it will be given, which, though the same essentially 
with the foregoing, will tend to make the meaning clearer 
by putting it in different words. 

When unexplained residual effects are detected, they are usu- 
ally to be attributed to unestimated remaining causes. 

Subduct from any phenomenon such part as is known by pre- 
vious inductions to be the effect of certain antecedents, and the 
residue of the phenomenon is the effect of the remaining ante- 
cedents. 

This method is not very available in ordinary affairs, nor, 
indeed, in any department is it generally valuable beyond 
its use for suggestion. When astronomers w T ere w T atching 
the recurrence of the eclipses of Jupiter's moons, it was dis- 
covered that while they occurred nearly at the predicted 
time, they did not occur exactly at it. It was an interesting 
question to discover the reason of this error. It was noticed 
that it was of itself subject to regular increase and diminu- 
tion. At a certain time the eclipse would occur as calcu- 
lated ; then it would begin slowly to fall behind, and this 
delay would gradually increase until it reached a maximum, 
when it would begin slowly to gain, until it returned to this 
point of agreement. Now the cause of the eclipse was well 
understood, and nothing was observed to conflict with the 
received theory. There was, however, this residual varia- 
tion after all causes had been estimated. Finally, it was 
suggested that possibly this variation might be due to the 
fact that light required time to pass through space. This 
was a cause that had not been considered. Indeed, the 
6* E 



66 EVERY-DAY ' REASONING. 

thought that light took time to move was itself new. But 
to confirm the theory, or rather as the thing which sug- 
gested it, the time of the eclipse was found to vary as the 
distance between this planet and Jupiter varied. The de- 
lay increased as the two planets went further and further 
apart, and diminished as Jupiter returned from apogee to 
perigee. Now, the difference of these distances was the di- 
ameter of the earth's orbit, and such a great distance would 
make the time which light required in its motion percep- 
tible, when it would not be perceptible in passing short dis- 
tances. Other experiments confirmed the suggestion thus 
made by the Method of Residues. 

The same line of argument has given reason to the hy- 
pothesis that all space is filled with a very attenuated ether. 
This was suggested as the explanation of the marked tardi- 
ness of the return of Encke's comet. All the data needful 
to determine its orbit and motion had been accurately ob- 
tained, and there ought, therefore, to have been no difficulty 
in fixing its periods. But it was noticed that it invariably 
fell behind the time which these calculations fixed for its 
return ; and when it returned, the most accurate observations 
gave no new elements, nor any change in the previous ele- 
ments, to account for this delay. Encke's comet, however, 
was the lightest of these heavenly bodies, and so its small 
amount of matter, compared with its volume, would make 
it very susceptible to retardation, from having to pass 
through the supposed ether of the heavenly spaces. The in- 
terference of the ether with its motion was similar in nature, 
but very much less in degree, to that offered by the air, when 
we try to throw a pith-ball to a great distance. If this ether 
exists, its presence is very difficult to prove, and yet this 
residual phenomenon gives it great plausibility. The vibra- 
tory theory of light seems to demand something of the same 
sort. 

The method of estimating the area of the circle, by mul- 



METHOD OF RESIDUES. 67 

tiplying its circumference by half its radius, was also sug- 
gested by a constant observation of residues. Thus, if in a 
circle we inscribe an octagon, and draw radii from the ex- 
tremity of each side, we will have eight triangles, whose area 
is the product of their base by half their altitude. The sum 
of these triangles differs from the surface of the circle only 
by the spaces included between the circle and the eight 
cords, which are the sides of the octagon. If now we double 
the number of sides, we will greatly diminish this external 
residue, and the sum of the sixteen sides will approach the 
length of the circumference. If now this process is indefi- 
nitely continued, and we have a polygon of an infinite number 
of sides, the sum of these sides will approximate, as we might 
say, infinitely near the circumference, and the altitude of 
each triangle approach infinitely near the length of the 
radius. If the two could be maple to exactly coincide, the 
circumference would be exactly the sum of the sides, and 
the altitude precisely equal the radius, in which case the 
area of the infinite-sided polygon would equal the area of 
the circle, and could be found by the multiplication of the 
circumference by half the radius. This method always 
seems open to the theoretical objection that this residue be- 
tween the sides of the polygon and the circle never can, even 
in infinity, absolutely disappear. It may, however, be a 
property of the circle, that its area is equal to its circumfer- 
ence multiplied by half its radius. In any case, this con- 
stant study of these residues furnished the suggestion by 
which the rule was reached. 

This explanation and illustration of this method will 
readily enforce the special rule for its employment. It is : 

Take cases, where the known antecedents and. consequents 
are best known and easiest estimated with exactness, and where 
the residues are fewest and best defined. 

The method will be of little avail, unless we are reason- 
ably certain of the amount of influence exerted t>y the 



68 EVERY-DAY REASONING. 

supposed known forces. If we do not know their power, we 
cannot know what the residue is at all. And if these resid- 
ual forces are very numerous or poorly defined, there is 
but little hope of valuable results. There are, however, 
cases in which all these complications are present. We 
cannot always get our cases cleared up and simplified to our 
mind, and must take them as we can get them. In social 
and political studies these complications are sometimes very 
great. We are, therefore, always to be on our guard against 
placing too much reliance on inductions only hinted at by , 
this method in the midst of multitudes of facts. In the 
history of chemistry, this method, however, has had its value 
as fully vindicated as in the department of astronomy. Thus 
when Arfwedson was analyzing a certain mineral, he made a 
sulphate from a small portion of what he supposed was mag- 
nesia, but, to his surprise, there was a small excess of weight 
beyond what the elements he had obtained, as he supposed, 
would account for. This residual phenomenon called^ for 
investigation, and the discovery of lithia, and the before un- 
known metal lithium, was the final result. The same method 
of investigating residues has been a very fruitful source of 
discovery of new metals. A very beautiful illustration of 
the application of this method is found in the department of 
physics. In the investigation of the nature of sound, its 
mode of propagation had been so well determined as to give 
very clear data from which to calculate its velocity in the 
air. But when it was attempted to verify the calculation 
by experiment, it was found to agree so well in the main, 
as to leave no doubt that the theory was correct, while yet 
it did not account for the whole velocity. This residual 
velocity was for a long time an extremely curious, and yet 
apparently insoluble, problem. At length the happy 
thought came to La Place, that this might arise from the 
heat, which ought to be developed by the condensation, 
which must necessarily take place at every vibration, by 



METHOD OF RESIDUES. 69 

which the sound is conveyed. This residual cause was, 
however, a matter capable of exact calculation, and when 
that calculation was made, it was found exactly to furnish 
a complete explanation of the residual velocity ; and so fur- 
nished a striking confirmation of the value of the Method 
of Residues, as well as of the general methods of induction. 
As an illustration of how, beforehand, the Method of Residues 
map be indicated, as the proper one to be adopted by inves- 
tigators of a particular subject, we quote from Whewell's 
History of the Inductive Sciences some suggestions in regard 
to the then present condition of inquiries into the laws and 
causes of tides. 

" Looking at this subject (the tides) by the light which 
the history of astronomy affords, we may venture to repeat 
that it will never have justice done it, till it is treated as 
other parts of astronomy are treated : that is, till tables of 
all the phenomena which can be observed are calculated by 
means of the best knowledge we at present possess, and till 
these tables are constantly improved by comparisons of the 
predicted with the observed fact, A set of Tide-observations 
and Tide-ephemerides of this kind would soon give to this 
subject the precision which marks the other parts of astron- 
omy; and would leave an assemblage of residual phenomena, 
in which a careful research might find the materials of other 
truths as yet unsuspected/ 1 

These illustrations will enforce the remark made at the 
outset of the treatment of this method, that its greatest value 
was for suggestions, By it we are enabled to clear away all 
needless matters, and so fix attention on those things where 
the desired truth seems to be concealed. Attentive inspec- 
tion of either of them may indicate novel and beautiful 
truths, but when we are able to eliminate from our observa- 
tions all known causes and effects, and so leave exposed 
alone the yet unknown connections of cause and effect, the 
probability of the detection of the truth is greatly increased. 



70 EVERY-DAY REASONING. 

Our vision is often hindered by the very great number of 
things exposed to our view, so that what we fail to recognize 
in the mass, we see and are able to examine minutely when 
it alone is left for inspection. There is a famous picture of 
two old dead trees, at one time said to stand on the island 
of St. Helena. On looking at the picture there seems to be 
nothing very peculiar about it, and you may even be told 
that there is the figure of a man on it, and yet be wltolly 
unable to discover it. If, however, your attention is called 
to the profile of Bonaparte, outlined by the trunks and 
branches of the two trees, you will scarcely be able to see 
much else in the picture beside that familiar form standing 
between the trees. Just so it is with us in the pursuit of 
truth. As *v T e look at the confused mass of facts, we may 
know that the mystery we seek to unravel is there, but we 
can scarcely hope to detect it in the crowd. When, however, 
all else is removed, and w*e come to inspect the remainders, 
these truths will so seem to stand out that it appears strange 
that any difficulty could be found in their discovery. All 
was dead tree with leafless limb before, but now in the 
midst there stands out the wonderful thing God has made. 

METHOD OF CONCOMITANT V4KIAII0NS. 

When a variation in a given antecedent is accom- 
panied BY A VARIATION OF A GIVEN CONSEQUENT, THEY 
ARE IN SOME MANNER RELATED AS CAUSE AND EFFECT. 

All the other methods require a possibility of the remo- 
val of certain causes. There are, however, some agents that 
cannot be wholly removed. No means known to man will 
enable us to free ourselves from the action of gravity. That 
strange force goes through all the obstacles we. can put in 
its path. So it will be very difficult to escape from some 
degree of heat, be it greater or less. In such cases the em- 
ployment of the methods that require the removal of causes 



METHOD OF CONCOMITANT VARIATIONS. 71 

is not practicable. We can only endeavor to disengage 
ourselves from their control, or neutralize the distracting 
force of their presence. So, also, there are some classes of 
subjects in which experimentation in any form is very diffi- 
cult. This is especially true in all historical studies. What 
then can be done? Resort must be had to this method, 
which does not require the removal of any cause, but aids 
us in seeing their effects even while in action and mixed 
with other causes, All that is required is that the intensity 
or quantity of the cause should vary. If it does, it would 
be a very remarkable thing indeed, if that variation did not 
show itself in a corresponding variation of the effect. Thus, 
for a simple illustration, take the effect of heat on iron. We 
have an iron bar with one end fixed, and we mark the length 
of it, and then heat it, and we find that it is longer now 
than before, We let it cool, and it begins at once to grow 
shorter. We heat again and it expands. We need nothing 
further to convince us that one of the effects of heat on iron 
is its expansion. That has been determined by this Method 
of Concomitant Variations, The increase of the cause is ac- 
companied by the increase of the effect. 

When we consider motion in absolute space, no reason 
can be assigned why it should not always continue in the 
same direction in which it may at any time be moving, Yet 
as a fact, we see almost no motion whatever in a straight 
line. All things are moving in curves, and for all terres 
trial motions there is a rapid tendency to come to a state of 
rest. Is, then, rest the natural state of bodies, and are curved 
lines the natural courses of motion ? Both of these questions 
have been answered in the negative by the Method of Con- 
comitant Variations.* Thus if we take the motions of bodies 
with which we can experiment, we at once recognize the in 
terference of the atmosphere as an obstacle tending speedily 
to bring bodies moving through it to a state of rest. When 
we try to run,- and especially try to run against the wind, 



72 EVERY-DAY REASONING. 

we feel the interference to be very great. If now we reduce 
this interference, by setting a pendulum in motion in a ves- 
sel from which the air is partially excluded, or from which 
part is pumped out, we find it will swing for a much longer 
time than it will in the open air. The more completely we 
remove the air the longer will the motion produced by the 
same amount of force continue. This increase of time, as 
the interference is diminished, points directly to the truth 
that the stoppage is due to hindrances, Another hindrance 
is found in the friction at the point where the pendulum is 
suspended; but this may also be very greatly reduced. 
The increase of time during which a pendulum will continue 
to oscillate, when these hindrances are so far as possible 
removed, is most remarkable. Borda prolonged the time 
during which a pendulum would move when so drawn from 
the perpendicular, that in the air it would come to rest in a 
few minutes, to more than thirty hours, by thus reducing 
the friction, and placing it in a vessel from which the air 
had been removed. This and all other experiments made 
tend to show that moving bodies only come to rest because 
their motion has been hindered by obstacles in their path. 
The same line of argument applied to projectiles gives the 
same conclusion with reference to curved motions. When 
the cannon-ball is shot from a tower it curves to the ground. 
But it meets, on leaving the cannon, two forces — the air re- 
sisting its passage, and gravity dragging it to the ground. 
Both of these are well enough known to have their effect 
exactly estimated, and when the experiment was made on 
as large a scale as possible, it was found that the curvature 
diminished in just the ratio in which these interfering forces 
were removed. By this suggestion, from the Method of 
Concomitant Variations, it followed that it might be that 
the true law was, that a body propelled by a force sufficient 
to secure a given rate of motion in a given direction, would 
follow a right line in that direction at that rate until inter- 



METHOD OF CONCOMITANT VARIATIONS. 73 

fered with by some obstructing or diverting force. If this 
was true, then it gave a basis for most interesting calcu- 
lations, since all curved motions must be accounted for by 
interfering forces. Many instances were accessible where 
these forces could be calculated, and, as confirming the 
theory, it was found that they exactly met the case calling 
for just the curve, which was actually described by the mov- 
ing bodies. In Newton's investigations, as to the effect of 
gravity, he proved that the orbit of the moon was exactly 
that which, according to these laws, would be described by 
a body of the volume of the moon, moving at its velocity, 
when drawn from the course of a straight line by a force 
equal to the attraction the earth exerts on it at its distance. 
The orbits of the heavenly bodies are not circles but ellipses, 
with the body around* which they revolve in one of the foci. 
Moving in such an orbit, they are much nearer the body at 
the centre at some times than at others, The earth is esti- 
mated to be three million miles nearer the sun when it is in 
its perihelion than when it is in aphelion. Here then is an 
opportunity for applying this Method of Concomitant Vari- 
ations on an immense scale. As the force of attraction in- 
creases as the square of the distance diminishes, the force 
exerted by the sun on the earth must sensibly increase as 
the earth comes from its aphelion, or point farthest from the 
sun, to its perihelion, or point nearest the sun, and unless this 
increased force is counteracted by an increase of velocity, 
the earth must inevitably fall into the sun. But both of 
these are ascertainable quantities, and we find that this in- 
crease of attraction is beautifully counteracted by just the 
increase of velocity needed to overcome it. So, on the other 
hand, as the earth moves away from the sun to that part of 
its orbit farthest from it, if its velocity was maintained, it 
must now as certainly fly off altogether as it was certain to 
fall into the sun before. Here again the equilibrium is 
maintained by its slowly diminishing rate of movement, so 
7 



74 EVERY-DAY REASONING. 

that the increase of attraction is matched by an increage of 
velocity, and the decrease of attraction is compensated by 
a decrease of velocity. 

These illustrations again lead us with ease and clearness 
to the fundamental principle on which this method is based, 
which is, that causes should act proportionately to their quart* 
tity or intensity, We have, therefore, this other statement 
of its general rule : When increasing or diminishing 

THE INTENSITY OF A CAUSE IS FOLLOWED BY THE IN- 
CREASE OR DECREASE OF ANY EFFECT, THEY ARE RELATED 
DIRECTLY OR INDIRECTLY TO EACH OTHER, This relation 

is not always an immediate relation to each other, as in 
many cases they may reach each other through some one or 
more intervening agents. Time and care may thus be re- 
quired in tracking out the route of tjiis action. An illus- 
tration of these intervening agents is found in the case of the 
ivory balls suspended in a row so as to touch each other* 
If the one at the end is swung back and let fall against the 
row, only the one at the other end will move. Now, although 
all the rest remain stationary when it flies out, yet the im- 
pulse, no doubt, was communicated through them from the 
first to it. This simple case is an example of what occurs 
in much more complicated forms in many other cases. If 
now we, by the increase or diminution of any cause, observe 
a corresponding increase or diminution of an effect, we may 
be reasonably sure that they are related, while we may not 
be sure of how many operations may intervene, 

Another case needs our attention also. There are cases 
where an increase of a supposed cause is followed by a de- 
crease of its supposed effect. This seems to contradict the 
method, and, of course, to be of little or no available use. 
On the contrary, however, it may lead to very valuable re- 
sults. It shows just as clearly as the other that there must 
be a relation between the two. Moreover, it suggests what 
that relation most probably is : namely, one of interference. 



METHOD OF CONCOMITANT VARIATIONS. 75 

Thus, if we have certain agents, A, B, C, D, at work with a 
given effect, X, produced, and we find that as D is increased 
X is diminished, and that the decrease of D is followed by 
the increase of X, the conclusion is very probable that D, 
instead of being either an active, dormant, or subordinate 
cause of X, is an obstacle whose entire removal would give 
a clearer view of the relations of the true agents, and whose 
presence is only useful in practical affairs as a regulator. 
Thus the tighter the brake is drawn in a car the slower its 
motion, and the more it is relieved the faster is its motion. 
This shows by its concomitant variations that, instead of the 
brake being a cause of the motion of the car, its office is to 
prevent or reduce it. 

As for the special rule to be remembered in the applica- 
tion of this method, it is the same as that of the Method of 
Difference. Maintain all the conditions as nearly identical as 
possible, except the increase or decrease of the hypothetical cause. 
The method is indeed a modification of the Method of Dif- 
ference, in that it considers minute differences of intensity, 
while the Method of Difference considers an entire absence 
of causes. The two are, however, sufficiently distinct to re- 
quire separate treatment, for, like addition and multiplica- 
tion, which are theoretically one, yet their applications are 
very different. So of this last method, it can be used with 
great effect when the other is not available. In the depart- 
ment of social science it is of very great value. Scarcely 
any other method is available to such questions as the influ- 
ence of education on crime. Every criminal knows some- 
thing, and no one knows everything. All that can be done, 
therefore, in investigating such matters, is to look at large 
numbers of instances, in the hope of detecting concomitant 
variations enough to indicate a law, and then watch its ap- 
plication. There are a large number of similar cases, such 
as the beneficial or injurious effects of legislation on rates of 
interest, and in regard to paupers and tramps. So in regard 



76 EVERY-BAY REASONING. 

to many questions of health and disease, no other method is 
available in the circumstances. 

These subjects, however, bring to light a very important 
qualification in regard to the conclusions we may reach, 
since the variations which may hold good for a certain 
amount of increase or diminution will not always hold good 
when we pass beyond that. The rule, that if a little is good 
more will be better, can hardly ever be trusted as true. 
How far it is true, is itself a very important problem. Just 
where the maximum of efficiency is reached is a very impor- 
tant matter to know. Every one familiar with theoretical 
and practical mechanics can readily recall instances where 
machinery, whose construction was exactly in accordance 
with the rules for the composition and resolution of forces, 
has utterly failed to work, because some new and unforeseen 
obstruction interfered, which was not indicated in the experi- 
ments on a small scale. Two lines may not diverge from 
each other enough in a short distance to make the differ- 
ence appreciable, while this difference may be very great 
when they are protracted to great lengths. The Method 
of Concomitant Variations is, therefore, to be cautiously 
employed when its results are assumed as true beyond the 
limits wherein it has been tested. 

FOUR METHODS ILLUSTRATED. 

It is proposed now to present two illustrations of these 
methods, and both shall be famous ones from the history of 
science. The first is the elegant series of experiments made 
by Sir Humphrey Davy, in the decomposition of water. At 
the time of which we speak, it was believed that water was 
composed simply of oxygen and hydrogen. When, how- 
ever, on one occasion, Mr. Davy was decomposing water by 
the galvanic current, he discovered an acid and an alkali 
on the poles of his battery. The question at once proposed 



FOUR METHODS ILLUSTRATED. 77 

itself as to the source of these. The decomposition of a salt 
would give them, but, so far as he knew, there was no salt of 
any kind in the water. However, he also knew that glass 
was a silicate of soda, and as the vessel containing the water 
was- glass, he suspected that its decomposition furnished the 
acid and the alkali. 4 True, he could see no mark of it, and 
he could feel no roughness, such as would probably have 
been found if the glass was decomposing, but the result 
seemed to point directly to it as the cause. To determine 
the question, he resolved to apply the Method of Difference, 
and the result was, that he got an answer by the Method of 
Agreement. He said, if it is the glass, and for the glass I 
substitute a gold vessel, the gold will not decompose, or if it 
should, being a metal, its result will not be an acid and an 
alkali. He, therefore, made the experiment, expecting to 
find no trace of either, when, to his surprise, he found both 
acid and alkali in as large quantities as before. From this 
it was evident that the glass was not the cause, for, by the 
Method of Agreement, when the glass was removed the 
effect remained, showing that the cause was not disturbed. 
After much thought another suggestion came to this effect, 
that the perspiration of the body was salty, and if he had 
allowed the water to touch his hands, the decomposition of 
that might account for the acid and alkali. Again he tried 
the Method of Difference, by carefully excluding all possi- 
bility of any perspiration reaching the water, and now re- 
peating the experiment, he found a perceptible decrease in 
the quantity deposited on the poles of the battery, but very 
considerable amount still there. Here was now an answer 
by the Method of Concomitant Variations. It pointed to 
the impurities of the water as the source of the acid and 
the alkali. The diminution of that source had decreased 
the result. If, however, this was correct, the Method of 
Residues would suggest that the remaining acid and alkali 
must be due to some remaining impurities. The next step 



78 EVERY-DAY REASONING. 

was readily suggested, for it was then, as now, a well-known 
fact that water from the earth's springs, or wells, almost 
always contains what are called natural salts of lime and 
other substances. Following out this hint, he determined 
to settle the question whether the acid and alkali were 
wholly due to the impurity of the w^ter, or whether water 
itself contained other elements besides mere oxygen and 
hydrogen. In either case, the result would be a valuable 
addition to knowledge. Here again he employed the 
Method of Difference, for now he took rain-water, the purest 
form in which Nature furnishes water, and then distilled it, 
hoping thus to get rid of every possible impurity. When, 
however, the experiment was repeated, there they were, but 
the quantity was greatly diminished. All four Methods now 
pointed to the same conclusion, namely, that notwithstand- 
ing all his precautions, he had still left some source of im- 
purity, and that this impurity was the cause of the slight 
remaining trace of acid and alkali. The Method of Agree- 
ment indicated it, because every impurity, as it was removed, 
showed that it had contributed its share to the original 
amount. The Method of Difference pointed the same way, 
for as the impurity was removed, the acid and the alkali 
were. The Method of Concomitant Variations indicated 
the same thing, since diminishing these impurities decreased 
the quantity. The Method of Residues concurred in sug- 
gesting that what remained was due to some remaining im- 
purity. It was not easy, however, to imagine what the 
source of that remaining impurity was. After much ponder- 
ing of the question, this happy thought occurred to the 
philosopher — May not the water absorb impurities from the 
air, which comes in contact with its surface ? This seemed 
at least not improbable. If the suggestion was' true, how- 
ever, that also was a source of impurity which could be 
entirely removed, and then the acid and alkali should dis- 
appear, or at least should be so far diminished as it was due 



FOUR METHODS ILLUSTRATED. 79 

to that source of impurity. Taking, again, therefore, his 
vessel of distilled rain-water, he placed it in the receiver of 
an air-pump, and at once pumped off the air, is completely 
as possible. When, now, the water was decomposed, neither 
acid nor alkali appeared, even in the smallest trace. This 
experiment was conclusive. The whole of ihe acid and 
alkali was due to the impurity of the water. Oxygen and 
hydrogen alone form w T ater. 

The other illustration of these four Methods will be taken 
bodily from Mill's Logic, in the words and co nments there 
given. Mill quotes it from Sir John Herschel's w r ork, en- 
titled a Discourse on the Study of Natural Philosophy, adding 
to Herschel's statement only a few brief remarks. The 
illustration is so elegant and so famous, that it is quoted by 
almost every writer on this subject, and is called Dr. Wells' 
Theory of Dew. 

" Suppose dew were the phenomenon proposer, whose cause 
we would know. In the first place we must determine pre- 
cisely what we mean by dew ; what the fact really is whose 
cause we desire to investigate. We must separate dew from 
rain, and the moisture of fogs, and limit the application of 
the term to what is really meant, w 7 hich is, the spontaneous 
appearance of moisture on substances exposed in the open 
air when no rain or visible wet is falling. This answers to 
a preliminary operation which will be characterized in the 
ensuing book, treating of operations or steps to induction. 
The state of the question being fixed, we come to the solu- 
tion. 

" Now, here we have analogous phenomena in the mois- 
ture which bedews a cold metal or stone when we breathe 
upon it ; that which appears on a glass of water fresh from 
the well in hot weather ; that which appears on the inside 
of windows when sudden rain or hail chills the external air ; 
that which runs down our walls when, after a long frost, a 
warm moist thaw comes on. Comparing these cases, we 



80 EVERY-DAY REASONING. 

find that they all contain the phenomenon which was pro- 
posed as the subject of investigation. Now all these in- 
stances agree in one point, the coldness of the object dewed, 
in comparison with the air in contact with it. But there 
still remains the most important case of all, that of noctur- 
nal dew : does the same circumstance exist in this case ? Is 
it a fact that the object dewed is colder than the air? Cer- 
tainly not, one would at first be inclined to say ; for what is 
to make it so ? But .... the experiment is easy ; we have 
only to lay a thermometer in contact with the dewed sub- 
stance, and hang one at a little distance above it, out of 
reach of its influence. The experiment has been, therefore, 
made ; the question has been asked, and the answer has been 
invariably in the affirmative. .Whenever an object contracts 
dew, it is colder than the air. 

" Here, then, is a complete application of the Method of 
Agreement, establishing the fact of an invariable connection 
between the deposition of dew on a surface, and the coldness 
of that surface compared with the external air. But which 
of these is cause and which effect ; or are they both effects 
of something else ? On this subject the Method of Agree- 
ment can afford us no light : we must call in a more potent 
method. * 

" That dews are accompanied with a chill is a common 
remark ; but vulgar prejudice would make the cold the 
effect rather than the cause. We must, therefore, collect 
more facts, or, which comes to the same thing, vary the cir- 
cumstances ; since every instance in which the circumstances 
differ is a fresh fact ; and, especially, we must note the con- 
trary or negative cases, i. e., where no dew is produced ; 
for we are aware that a comparison between instances of 
dew, and instances of no dew, is the condition necessary to 
bring the Method of Difference into play. 

" Now, first, no dew is produced on the surface of polished 
metals, but it is very copiously on glass, both exposed with 



FOUR METHODS ILLUSTRATED. 81 

their faces upwards, and in some cases the under side of a 
horizontal plate of glass is also dewed. Here is an instance 
in which the effect is produced, and another instance in 
which it is not produced ; but we cannot yet pronounce, as 
the canon of the Method of Difference requires, that the 
latter instance agrees with the former in all its circumstances 
except one ; for the differences between glas ; and polished 
metals are manifold, and the only thing we can as yet be 
sure of is, that the cause of dew will be found among the 
circumstances by which the former substance is distinguished 
from the latter. But if we could be sure that glass, and 
the various other substances on which dew is deposited, have 
only one quality in common, and that polished metals and 
the other substances on which dew is not deposited have also 
nothing in common but the one circumstance, of not having 
the one quality which the others have; the requisitions of 
the Method of Difference would be completely satisfied, and 
we should recognize, in that quality of the substances, the 
cause of dew. This, accordingly, is the pr/th of inquiry 
which is next to be pursued. 

" In the cases of polished metal and polished glass, the 
contrast shows evidently that the substance has much to do 
with the phenomenon ; therefore let the substance alone be 
diversified as much as possible, by exposing polished sur- 
faces of various kinds. This done, a scale of intensity be- 
comes obvious. Those polished substances are found to be 
most strongly dewed which conduct heat worst ; while those 
which conduct well resist dew most effectually. The compli- 
cation increases ; here is the Method of Concomitant Varia- 
tions called to 'our assistance ; and no other method was 
practicable upon this occasion ; for the quality of conduct- 
ing heat could not be excluded, since all substances conduct 
heat in some degree. The conclusion is that, other things 
being equal, the deposition of dew is in some proportion to 
the power which the body possesses of resisting the passage of 

F 



82 EVERY-DAY REASONING. 

heat ; and that this, therefore, (or something connected with 
this,) must be at least one of the causes which assist in pro- 
ducing the deposition of dew upon the surface. 

" But if we expose rough surfaces instead of polished, we 
sometimes find this law interfered with. Thus, roughened 
iron, especially if painted over or blackened, becomes dewed 
sooner than varnished paper ; the kind of surface, therefore, 
has a great influence. Expose, then, the same material in 
very diversified states as to surface, (that is, employ the 
Method of Difference to ascertain concomitance of varia- 
tions,) and another scale of intensity becomes at once appa- 
rent, those surfaces which part with their heat most readily by 
radiation, are found to contract dew most copiously. Here, 
therefore, are the requisites for a second employment of the 
Method of Concomitant Variations ; which in this case also 
is the only method available, since all substances radiate 
heat in some degree or other. The conclusion obtained by 
this new application of the method is, that cceteris paribus 
the deposition of dew is also in some proportion to the power 
of radiating heat ; and that the quality of doing this abun- 
dantly (or some cause on which that quality depends) is 
another of the causes which promote the deposition of dew 
upon the substance. 

" Again, the influence ascertained to exist of substance 
and surface leads us to consider that of texture : and here 
again we are presented on trial with remarkable differences, 
and with a third scale of intensity, pointing out substances 
of a close, firm texture, such as stones, metals, &c, as unfa- 
vorable, but those of a loose one, as cloth, wool, velvet, eider- 
down, cotton, &c, as eminently favorable to the contraction 
of dew. The Method of Concomitant Variations is here, for 
the third time, had recourse to ; and, as before,- from neces- 
sity, since the texture of no substance is absolutely firm or 
absolutely loose. Looseness of texture, therefore, or some- 
thing which is the cause of that quality, is another circum- 



FOUR METHODS ILLUSTRATED. 83 

stance which promotes the deposition of dew ; but this third 
cause resolves itself into the first, viz., the quality of resist- 
ing the passage of heat ; for substances of loose texture are 
precisely those which are best adapted for clothing, or for 
impeding the free passage of heat from the skin into the air, 
so as to allow their outer surfaces to be very cold while they 
remain warm within ; and this last is, therefore, an induc- 
tion (from fresh instances) simply corroborative of a former 
induction. 

" It thus appears that the instances in which much dew is 
deposited, which are very various, agree in this, and, so far 
as we are able to observe, in this only, that they either 
radiate heat rapidly or conduct it slowly : qualities between 
which there is no other circumstance of agreement, than 
that by virtue of either, the body tends to lose heat from 
the surface more rapidly than it can be restored from within. 
The instances, on the contrary, in which no dew, or but a 
small quantity of it, is formed, and which are also extremely 
various, agree (so far as we can observe) in nothing except 
in not having this same property. We seem, therefore, to 
have detected the sole difference between the substances on 
which dew is produced, and those on which it is not pro- 
duced. And thus have been realized the requisitions of what 
we have termed the Method of Difference, or the combined 
use of the Methods of Agreement and Difference. The ex- 
ample afforded of this indirect Method, and of the manner in 
which the data are prepared for it by the Methods of Agree- 
ment and of Concomitant Variations, is the most important 
of all the illustrations of induction afforded by this most 
interesting speculation. 

" We might now consider the question, upon what the 
deposition of dew depends, to be completely solved, if we 
could be quite sure that fehe substances on which dew is pro- 
duced differ from those on which it is not, in nothing but in 
the property of losing heat from the surface faster than the 



84 • EVERY-DAY REASONING. 

loss can be repaired from within. And, although we never 
can have that complete certainty, this is not of so much 
importance as might at first be supposed ; for we have, at 
all events, ascertained that even if there be any other quality 
hitherto unobserved which is present in all the substances 
which contract dew,' and absent in those which do not, this 
other property must be one which, in all that great number 
of substances, is present or absent exactly where the property 
of being a better radiator than conductor is present or absent; 
an extent of coincidence which affords the strongest presump- 
tion of a community of cause, and a consequent invariable 
coexistence between the two properties ; so that the property 
of being a better radiator than conductor, if not itself the 
cause, almost certainly always accompanies the cause, and 
for purposes of prediction, no error will be committed by 
treating it as if it were really such. 

" Reverting now to an earlier stage of the inquiry, let us 
remember that we had ascertained that, in every instance 
where dew is formed, there is actual coldness of the surface 
below the temperature of the surrounding air ; but we were 
not sure whether this coldness was the cause of dew, or its 
effect. This doubt we are now able to resolve. We have 
found that, in every such instance, the substance must be 
one which, by its own properties or laws, would, if exposed 
in the night, become colder than the surrounding air. But 
if the dew were the cause of the coldness, that effect would 
be produced in other substances, and not solely in tho'se 
whose own laws suffice to produce it whether there were dew 
or not. That supposition, therefore, is repelled. But there 
were only three suppositions possible ; the dew is the cause 
of the coldness ; both are caused by some third circumstance ; 
or the coldness is the cause of the dew. The first is refuted. 
The second is inapplicable: the cause of the coldness is a 
known cause; a radiation from the surface greater than can 
be supplied by conduction : now this, by its known laws, 



FOUR METHODS ILLUSTRATED. 85 

can produce no direct effect except coldness. There remains 
only the third supposition, that the coldness is the cause of 
the dew : which, therefore, may be considered as completely 
made out. 

"This law of causation, already so amply established, 
admits, however, of most efficient additional corroboration 
in no less than three ways. First, by deduction from the 
known laws of aqueous vapor when diffused through air or 
any other gas ; and although we have not yet come to the 
Deductive Method, we will not omit what is necessary to 
render this speculation complete. It is known by direct 
experiment that only a limited quantity of water can remain 
suspended in the state of vapor at each degree of tempera- 
ture, and that this maximum grows less and less as the 
temperature diminishes. From this it follows, deductively, 
that if there is already as much vapor suspended as the air 
will contain at its existing temperature, any lowering of that 
temperature will cause a portion of the vapor to be con- 
densed and become* water. But, again, we know deductively, 
from the laws of heat, that the contact of the air with a 
body colder than itself, will necessarily lower the tempera- 
ture of the stratum of air immediately applied to its sur- 
face ; and will therefore cause it to part with a portion of its 
water, which accordingly will, by the ordinary laws of gravi- 
tation or cohesion, attach itself to the surface of the body, 
thereby constituting dew. This deductive proof, it will have 
been seen, has the advantage of proving at once, causation 
as well as coexistence ; and it has the additional advantage 
that it also accounts for the exceptions to the occurrence of 
the phenomenon, the cases in which, although the body is 
colder than the air, yet no dew is deposited ; by showing 
that this will necessarily be the case when the air is so un- 
dersupplied with aqueous vapor, comparatively to its temper- 
ature, that even when somewhat cooled by the contact of 
the colder body, it can still continue to hold in suspension 
8 





86 EVERY-DAY REASONING. 

all the vapor which was previously suspended in it : thus ill 
a very dry summer there are no dews, in a very dry winter 
no hoar frost. Here, therefore, is an additional condition 
of the production^ of dew, which the methods we previously 
made use of failed to detect, and which might have remained 
still undetected, if recourse had not been had to the plan of 
deducing the effect from the ascertained properties of the 
agents known to be present. 

" The second corroboration of the theory is by direct ex- 
periment, according to the canon of the Method of Differ- 
ence. We can, by cooling the surface of any body, find in 
all cases some temperature (more or'less inferior to that of. 
the surrounding air, according to its hygrometric condition) 
at which dew will begin to be deposited. Here, too, there- 
fore, the causation is directly proved. We can, it is true, 
accomplish this only on a small scale ; but we have ample 
reason to conclude that the same operation, if conducted in 
Nature's great laboratory, would equally produce the effect. 

" And, finally, even on that great scale we are able to 
verify the result. The case is one of those (rare cases, as 
they will be found to be) in which Nature works the ex- 
periment for us in the sarnie manner in which we ourselves 
perform it ; introducing into the previous state of things a 
single and perfectly definite new circumstance, and mani- 
festing the effect so rapidly that there is not time for any 
other material change in the preexisting circumstances. 
Let lis quote again Sir John Herschel : It is observed that 
dew is never copiously deposited in situations much screened 
from the open sky, and not at all in a cloudy night ; but if 
the clouds withdraw even for a few minutes, and leave a clear 
opening, a deposition of dew presently begins, and goes on in- 
creasing. . . . Dew formed in clear intervals will often even 
evaporate again when the sky becomes thickly overcast. 
The proof, therefore, is complete, that the presence or ab- 
sence of an uninterrupted communication with the sky causes 



CLASSIFICATION BY THE FOUR METHODS. 87 

the deposition or non-deposition of dew. Now, since a clear 
sky is nothing but the absence of clouds, and it is a known 
property of clouds, as of all other bodies between which and 
any given object nothing intervenes but an elastic fluid, 
that they tend to raise or keep up the superficial tempera- 
ture of the object by radiating heat to it, we see at once that 
the disappearance of clouds will cause the surface to cool ; 
so that Nature, in this case, produces a change in the ante- 
cedent by definite and known means, and the consequent 
follows accordingly: a natural experiment which satisfies 
the requisitions of the Method of Difference." 

A careful study of this example will justify in our minds 
the remark of Sir John Herschel, in quoting it, when he 
calls it " one of the most beautiful specimens of inductive 
experimental inquiry lying within a moderate compass." 
It is also worthy of remark, that while it so perfectly illus- 
trates the scientific application of these methods, it at the 
same time exemplifies the use of these methods in the prac- 
tical affairs of e very-day life. Although we may not recog- 
nize the fact, and may be wholly unconscious of its truth, 
we are every day coming to conclusions, and acting on them, 
which, if we could trace out the mental processes by which 
we reached them, we would find based on just such logic. 
For discipline, therefore, nothing can be better than to in- 
vestigate the beliefs we entertain, and, reviewing the grounds 
of them, determine to which of these methods each step or 
argument belongs. Ambitious students should pay great 
heed to this last suggestion. If followed it will enable them 
with promptness and clearness to analyze the argument, 
and expose the fallacy or confirm the position of -those with 
whom they come in contact. 

CLASSIFICATION BY THE POUR METHODS. 

This is the most suitable place to introduce some remarks 
on a few matters which cannot be exhaustively treated in 



88 EVERY-DAY REASONING. 

so brief a work. We first return to the subject of Classifi- 
cation, on which already (page 23) something has been said. 
The difficulty of this matter has been recognized by all 
students of nature. There is general agreement that it is a 
natural tendency of the mind to group things in classes. By 
this means it relieves itself of a vast amount of valueless 
labor, in that it burdens itself only with the peculiarities in 
which things agree, or are marked by their disagreement, 
and so needs not to recollect the unimportant differences. 
When it reaches the groupings of objects, as nature has as- 
sociated them, the task is greatly simplified. To reach that 
natural or scientific classification is, however, very often a 
long -and tedious process. Two things are involved in it, 
both of which are difficult. There must first of all be a set- 
tled principle of classification. The peculiarity of the Lin- 
nsean system of botanical classification was mainly the adop- 
tion of the flowers, with their stamens and pistils as the basis. 
Dr. Agassiz, in his work on "Methods of Study in Natural 
History," claims it as one of his most important contributions 
to the science of zoology, that he recognized form as deter- 
mined by structure as the true basis of classification of 
families. This was a remarkable instance of the value of a 
basis, for as the distinction was one of form, it readily struck 
the eye, and so was recognized ; and the secondary work of 
locating the individuals in their appropriate families had 
proceeded quite satisfactorily before the true reason for the 
division was found. That the work could not be brought 
to perfection without such a basis was very evident, since 
different authors made such different assignments to certain 
individuals, and the same author so frequently changed his 
own assignments in newer editions of his works. 

What now were all these philosophers doing but repeating 
the process of comparison, and testing the results by the 
Methods of Agreement and Difference. The basis they 
sought was such a set of marks as would result in giving a 



CLASSIFICATION BY THE FOUR METHODS. 89 

class, where the presence of each mark would be the sign of 
all the other marks. Here, too, the Method of Residues 
served a good purpose, since, when all those which properly 
and evidently belonged to the ascertained classes were taken 
out, and the others left by themselves, the as yet unknown 
classes among them were detected, and whether one or many, 
the logical process was the same. Nor is the Method of 
Concomitant Variations without its use in this same work 
of classification. In chemistry the basis of distinction 
among the acids is due to the amount of oxygen which they 
contain. So the different kinds of iron are supposed to be 
marked by the amount of carbon found in them ; steel hav- 
ing more carbon than refined iron, and malleable iron less 
carbon than cast iron. All these methods are thus of very 
great value, and are constantly used in this first and very 
difficult work of determining the basis of the classification. 

This done we come to the next step, which is much more 
simple than this first process. The task now is to go over 
each individual, and, on the basis heretofore adopted, locate 
the proper place of the individuals in this arrangement of 
nature. Here the work is almost wholly one of applying 
the Methods of Agreement and Difference. If we have the 
right marks, by which each class is characterized, then care- 
ful inspection will tell us in each case to which class a given 
individual belongs. Thus, if you bring to a conchologist a 
lot of shells, and watch him at his work of cataloguing and 
describing them, you will see him go through exactly the 
process we have described. He will take them, one after 
another, and looking them over for the features by which 
the several orders, families, genera, and species are to be 
distinguished, he will assign them to their proper place, and 
give them the agreed upon name, which shall indicate their 
possession of these characteristics. So, if you take a seed to 
a botanist, he will open it, and will tell you that, if planted, 
it will grow from without, by adding rings, " because," and 
8* 



90 EVERY-DAY REASONING. 

then he will follow up that word because, by giving his rea- 
son ; namely, that it agrees with the seeds of exogenous 
plants, in that it is dicotyledonous, or has two seed lobes. 
He will also tell you that it will probably have leaves with 
veins crossing each other, which is another peculiarity of 
plants of that class. All this is obviously by the Method of 
Agreement, and he will decide as to all the other seeds you 
may bring him by the same process. The whole operation 
is one of comparison. The decision is reached by the Meth- 
ods of Agreement and Difference, and success depends on 
the intelligence with which these methods are employed. 
No progress whatever can be made without their use. 

This enables us to repeat, with very decided emphasis, 
the importance of careful observation. It is easy to accept 
superficial inspection for satisfactory examination, and pro- 
ceed thus on utterly incorrect suppositions. Scientific suc- 
cess and greatness depends largely upon the exactness and 
certainty of the comparisons made. Every year hundreds 
.of lives are lost, because ignorant or heedless physicians, 
hastily examining their patients, decide that it is one form 
of disease from whichVthey are suffering, and treat them for 
that, of course, without success, because they have not had 
it, and do not have it, and are dying of an entirely distinct 
malady. The case presented the usual symptoms which 
identify the disease, if the knowledge and care requisite to 
discover it had been used ; but that knowledge was not 
possessed, and that requisite care was not taken, and the 
patient died — the fault all belonging to the doctor. Al- 
though the results have not been so fatal and alarming, 
yet they have been just as truly the result of incapacity in 
the domain of natural history. Theories, classifications, and. 
hypotheses have followed each other in rapid succession, 
whose only basis was the superficial character of the study 
of their authors. In political life the same is constantly 
occurring. Windy politicians, catching a faint notion of 



CLASSIFICATION BY THE FOUR METHODS. 91 

some resemblance between the present conditions of public 
affairs and the circumstances that produced some great pros- 
perity or calamity before in history, claim public attention, 
and the mass of men, being as heedless and unscientific as 
themselves, follow their lead, and the end is other disasters, 
produced wholly by the impetuous ignorance of leaders and 
their followers. Reliable conclusions can only be reached 
by the classification of all the circumstances into the three 
divisions of causes — subordinate, dormant, and active ; and 
then, by the Methods of Agreement and Difference, deter- 
mining by careful comparison whether the agreements cover 
all the really essential causes, and whether the- differences 
are such as <to fatally interfere with the result. In the long 
run, remembering how inexorably nature's causes work out 
their true effects, our work of reasoning is very largely clas- 
sificatory. If we are correct as to the group of causes to 
which those at work in any case belong, we will not need to 
doubt the certainty of the result. 

The remarks on Classification already made may be 
summed up in three important rules. 

Rule First. — The Classification mast proceed on a defi- 
nite principle, which must be maintained throughout 

Rule Second. — The classes must include all the inferior 
classes or all the individuals. The classes must make tip the 
whole. 

Rule Third.— The classes must exclude each other ; that is, 
it must be impossible for any individual to be in more than one 
class of the same grade. 

These rules are those usually given for division, but divi- 
sion is only the reverse of classification. Division takes 
things in the aggregate, and separates them into groups ; 
while classification takes the individuals as found in nature, 
and combines them into groups. In both cases the above 
must be observed, and a regular, systematic gradation of 
groups maintained. All the individuals should find their 



92 EVERY-DAY REASONING. 

places in one of the lowest rank of classes, and these classes 
be combined into larger and higher groups, and so to the 
highest. 

ANALYSIS. 

The discussion of this subject is here introduced, not as 
being inseparably connected with this part of the present 
treatise, but as so indirectly connected, as to make it appro- 
priate; and so important as to make its presentation valuable. 
There is so much fallacious reasoning, based upon insufficient 
analysis, that the subject must be left incomplete, without 
some rules for the proper conducting of analysis. What 
then is analysis ? 

Analysis is the process of decomposing compound bodies, so 
that they are resolved into the elements of which they are made 
up, and determining in what proportions and relations these 
elements must be combined, in order to form the original sub- 
stance. All parts of this definition are important. Of 
course analysis may be attempted, but cannot be accom- 
plished with simple elements. It only undertakes to resolve 
those bodies, which are made up of simple elements, into 
the various uncompound substances of which they consist. 
But more is required in analysis than to determine that in 
a given compound body a certain substance enters as an 
element. That is one step, and an important step, too, in 
analysis, and is part of what is known as qualitative analy- 
sis. To complete, however, even qualitative analysis, this 
further labor is required ; namely, of determining all the' 
elements that enter into its composition. If we take a piece 
of limestone, we get some information when we determine' 
that there is calcium in it, and we have more when we learn 
that there is carbon in it. But this is not enough. Very 
many specimens of limestone also have iron ore in them, 
and some have magnesia, and these iron ores and magnesia 
have many other elements combined with them. Sufficient 



ANALYSIS. 93 

analysis must determine what are the elements, and the only 
elements present in that particular specimen which has been 
furnished. How is such a conclusion in any way possible 
of attainment? Here we rely on the methods of Agree- 
ment and Difference. We depend in the whole process on 
the uniformity of nature's agents and operations. In the 
case of the limestone, we conclude that calcium, carbon, 
oxygen, iron, and the like, are present, because the same 
manifestations are found that these substances have always 
indicated heretofore. Because these substances agree in their 
chemical, physical, and mechanical properties with those 
with which we are familiar, we are assured of their identity. 
When we undertake the second step of analysis, and try 
to answer the question how much of eaeh of these, as well as 
what substances, are found in the compound, the difficulty 
is greatly increased. This will be seen when we reflect that 
two new sources of error are now to be encountered. The 
first is that, in our process of analysis, we may ourselves 
introduce into the case elements that were not there before, 
and we be ignorant of their amount, or even of their pres- 
ence ; and so be led to fix on them as part of the original 
compound*. In this way an additional quantity of some ele- 
ment, already present, may also be introduced, vitiating 
thus the whole process. On the other hand, we are liable to 
have elements, or a certain portion of the elements of the 
original compound escape, without our measuring them, or 
even detecting their existence at all. For example, in 
chemical analysis, it is extremely difficult to procure per- 
fectly pure chemicals ; and yet, without these, the whole is 
utterly valueless, since the impurities of the chemicals will, 
in a greater or less degree, affect the results, and when these 
results are thus affected by new and unknown agents, they 
are of no use whatever. So, in distillation and filtration, it 
is easy for substances to escape, and no conclusive results 
are reached unless that escape is noticed and accurately 



94 EVERY-DAY REASONING. 

measured. Suppose the subject under investigation is magnet 
ism, and to find out what magnetism is, we proceed to ana- 
lyze a piece of soft, unmagnetized iron ; it would be of no 
avail except to show what it is not. Is it much better to 
analyze a dead carcass to find out what life is? In all 
these steps it is by the same methods that we proceed, so far 
as the logic is concerned. It is comparing things together, 
to see wherein they agree and wherein they differ. Our 
analysis is aimed at fixing these points. 

Mere qualitative and quantitative analysis, however, is 
not enough to answer all our questions. We shall greatly 
err, if we suppose that the same elements, and the same 
amounts, will always produce the same compounds, and act 
in the same way. To illustrate this: there is a kind of 
chemical combination that will take place between certain 
substances, just when they are disengaged from one combi- 
nation, and before they enter into another, or when they are, 
as it were, in transitu. It will not occur before or after that 
particular nick of time when they are in what chemists 

call the nascent state. Is not the relation of the elements 

» 

their condition at that time, therefore a most important 
matter? Four very well known elements seem to make up 
almost the whole of organic bodies ; namely, carbon, hydro- 
gen, oxygen, and nitrogen. Besides these, there are present 
phosphorus, calcium, and other well known inorganic ele- 
ments, in larger or smaller quantities. But wherein lies the 
difference between them in their organized and unorganized 
condition ? We may not say positively, that it is in the re- 
lations under which they are combined, for it is not certainly 
known wherein it consists. It is strongly suspected that it 
is merely a difference of relation. The indications all point 
that way. If it could be proved so it would be a valuable 
point of knowledge gained. If it should so turn out, it is 
obvious that the question now left for solution is not one of 
qualitative analysis, nor yet of quantitative analysis, but one 



ANALYSIS. 95 

of relative analysis. Once a druggist, who had prepared 
for me a medicine, according to a physician's prescription, 
came in great haste, and asked that it should be exchanged 
for another bottle, which he brought with him. Of course 
suspicion was at once aroused, that he had, at first, given 
the wrong medicine, and that possibly serious consequences 
might follow the single dose administered from the first mix- 
ture. On inquiry, however, I found that the physician, in 
writing the prescription, had placed the elements in the 
wrong order ; so that as they were combined, some of them 
were precipitated, instead of being held in solution, and so, 
while the first mixture had no injurious drugs in it, there 
were some medicinal elements that were absent which were 
intended to be in it. When the drugs were combined in 
another order, the solution was perfect, the compound clear, 
and no sediment in the bottom of the viaL Here again it 
was a matter of relation, and an analysis that would have 
given the exact quantity of each element used, would 
not have determined all that was needful to know. The 
analysis and determination of the relations would be not 
less important than either of the others. 

These considerations make it clear that some method of 
testing and proving the completeness of our analyses is of 
very great moment. Mere analysis will not do, for while by 
it we may find out certainly that certain things are present, 
it can rarely be so conducted as to exclude the possibility 
that others have escaped our detection. Moreover, it gives 
us little knowledge of the relations and historical circumr 
stances under which the combination was formed. Another 
method, however, is available, and while, perhaps, not imme- 
diately and always conclusive that our analysis is complete, 
yet it greatly increases our certainty, by very greatly di- 
minishing the liability to the intrusion of foreign substances. 
This additional step is synthesis. As analysis decomposes 
substances into their elements, so synthesis is the reverse 



96 EVERY-DAY REASONING. 

process of combining these elements, so as to reform the 
original compound. If by taking the substances, which by 
our analysis we have detected as entering into the compo- 
sition of a substance, we Can by them reconstruct that which 
we have torn down, we are reasonably sure of the exactness 
of our knowledge. Suppose a man asserts that he under- 
stands clock-work, and, to test him* you give him a clock, 
and after carefully taking it apart, he immediately puts it- 
properly together again, so that it will run correctly, you 
ask no further proof. If, however, when he thinks he has 
put it together it will not run, that is just as conclusive 
against him as the other result was for him. So when we 
analyze water we find one part oxygen and two parts hydro- 
gen ; and when we mix one part oxygen with two parts of 
hydrogen, we are able to recombine them by explosion, and 
the result is water. These illustrations might be greatly 
multiplied, but as the subject will come up again, when we 
treat of Tests of Induction, it may be dismissed now, by 
repeating, that no analyses can be finally accepted as con- 
clusive, which do not include qualitative, quantitative, and 
relative analysis ; and that all analysis must be proved by 
synthesis or recomposition* 

THE QUESTIONS OP INDUCTIVE LOGIC. 

The natural method of procedure, in treating of a subject, 
is to map out the field as almost the first thing done. This 
course, however, labors under the disadvantage of unpre- 
paredness on the part of the student. Many advantages are 
gained by securing some familiarity with the theme, before 
we call attention to the determinate field of investigation. 
In this work we have adopted both methods. Early in our 
work we saw that the special field of inductive logic was 
Gaused Truth, as distinguished from both Necessary Truth 
and Error. Having now attained some familiarity with our 



THE QUESTIONS OP INDUCTIVE LOGIC. 97 

subject, we are prepared to fix definitely before us the ques- 
tions which are proper to ask in our inductive logic, and 
which, up to the limit of knowledge in each branch of sci- 
ence, it is able to answer. 

The Duke of Argyll, in his work " The Reign of Law/' 
undertakes to limit scientific knowledge to answering three 
questions, What? How? and Why? It is possible that, by 
a sufficient enlargement of the meaning of these, they may 
be considered exhaustive ; but there are at least three other 
questions that are always being asked by the human mind, 
and their answer more or less affects the answers of those 
given above. And herein lies the difficulty in their proper 
classification, for they may be asked under or in connection 
with each of them. These questions are, Who? Where? 
and When ? We must consider all of these. Beginning 
then with the first, The What is answered by the facts — by 
knowledge gained through inspection. Our sources for that 
are either in what we learn ourselves, or what others have 
learned by the powers of mind and body, and put on record. 
Two things, however, always connect themselves with every 
fact, and this knowledge will go to make up its character. 
These are the conditions of Space and Time. All caused 
truth connects itself with these conditions, so that while 
necessary truth is true, and equally true in all space and at 
all times, the truth of caused truth may be said to be de- 
pendent on these. What is true in one place is not true in 
another, and what is true at one time may never have been 
true before nor since. Complete knowledge, therefore, of 
the What must include also the Where and the When. Thus, 
there is no doubt that, within certain distance, the load- 
stone will attract soft iron, but the strength of that attrac- 
tion is measured by the matter of distance in space. So the 
matter of time has very much to do with all such matters 
as the growth of plants, and the effects of geologic forces. It 
is, therefore, a very unsatisfactory piece of information to 
9 G 



98 EVERY-DAY REASONING. 

say that a certain valley has been filled up. We also want 
to know how it was located, and how long it required for 
this process to complete the work. So in all cases where 
the information can be obtained, answers to both these ques- 
tions are important. The answer to the question of space, 
the Where, can always be secured, if it is a matter of knowl- 
edge at all, inasmuch as everything that is caused is caused 
in some place. It is equally true that it must have been 
caused at some time, but the time may not be so easily as- 
certainable, since the effect may continue after the fact, and 
so enable us to see that it was done, and where it was don&, 
but not when it was done. Thus, if I see a smooth-washed 
stone, I may know that the location of it was at some time 
submerged, but when that occurred I cannot tell from these 
facts. 

When now we pass to the second of the three questions 
mentioned by the Duke of Argyll, we have another collat- 
eral question rising into importance. It might, indeed, 
have been asked in connection with the What, but its an- 
swer would have been very difficult, so long as we rigidly 
excluded both the How and the Why. When we come to 
these two, however, the question Who is always pressing us. 
When I look at the beaver's dam, and note how it is con- 
structed, I can at once exclude from the possible agents 
mere chance or vegetable growth. The same is true when I 
look at the method on which the bird's nest is built. The 
Where and the When are still important, and every truly 
scientific observer will take pains to ascertain and record 
them, but not less important is the information as to the 
Who. Thus in the case of the beaver's dam, although the 
naturalist is sure it was not an accident, and did not grow, 
it deeply interests him to know what sort of an animal did 
construct it, and what trait of its nature and instinct is 
gratified by it. He learns the habits of birds from seeing 
them build their nests and nurture their young. This very 



THE QUESTIONS OF INDUCTIVE LOGIC. 9 ( J 

question demands 'an agent, whose method it asks, and so, 
even if we may not assign a rational agency in each case, 
there must, at least, be a real agent. Unless there is an 
actor, there can be no How to his acting. So no more can 
there be a question How, if there is no efficiency in causa- 
tion. If the relation of cause and effect is mere sequence or 
succession, all is accident, and there is and can be no How 
in the case. 

All argument on this subject is better deferred, to come up 
under the third question, Why. Very many philosophers 
assert that there is no such question in science as the why, 
or the wherefore. This is true of the whole school who 
hold to what is known as the positive philosophy. But, 
however, men may say it ought not to be asked, and no 
attempt made to answer it, the mind always has asked it, 
and it is therefore to be presumed always will. Just as 
surely as men reason, so surely they will find this question 
coming up to their own minds, and pressing itself upon them 
from the lips of others. If, therefore, any argument as to' 
the field of scientific inquiry may be drawn from the hunger- 
ings of the mind, this question cannot be in any wise ex- 
cluded. Nature's normal appetites do not often lead us 
astray. Even the philosophers of the positivist school are 
constantly appealing indirectly to this same principle. 
Even Compte could construct a system of education and 
government, and when you ask for the reason for his adjust- 
ments and regulations, there they are with their why and 
wherefore. No man can carry on a day's work without 
constantly having before his mind the object sought to be 
accomplished by each act. When, then, he comes to investi- 
gate other things, he instinctively proceeds on the principle 
that there must also have been some object before the mind 
of the doer. Moreover, this question, Why, receives abun- 
dant answer. Often it is the only question that can be satis- 
factorily answered. In multitudes of instances it receives 



100 EVERY-DAY REASONING. 

much fuller and clearer answer than the preceding question, 
How. Thus take the naturalist, studying the body of a bird. 
How that bird was made, and whence the origin of its 
species, are questions of very great difficulty ; but he can see 
a reason for the structure of almost every bone and muscle 
of its frame, and the most odd and exceptional peculiarities 
reveal for themselves a reason. "Who will tell us how the 
human hand was made, and give us any reasonable ground 
for faith in his assertions, if we refuse all notion of its uses? 
Yet anychild can understand why its structure should be 
as it is, and what great advantages we derive from its struc- 
ture. So in almost every case, the extent and value of the 
knowledge which is connected with this question, Why, is far 
beyond that of the How, which all admit is a scientific ques- 
tion. Anatomy is the science of the structure of the body. 
Physiology treats of the office of the several parts, and 
hygiene of the means for preserving their healthy action. 
What now is physiology, but the answer to the question 
why, asked of our anatomist ? Its importance none can dis- 
pute. So take the fact of the qualities, quantities, and dis- 
tribution of the metals, and no man can tell how they were 
distributed, or how it comes that iron, which is so much 
more available for the uses of man than gold, is so much 
more abundant, and more universally distributed. All can 
see at a glance that gold never could take the place of iron 
in the economic uses of man. A why for all this is not dif- 
ficult to give, but to tell how it was brought about, is not 
yet accomplished. A ready answer comes, if we ask why it 
is so much easier to answer this question, Why, than the ques- 
tion How ? The causes that produced a given result, work 
their result, and then pass away. The result, however, re- 
mains. The how it was done is thus a matter of history, 
and if no record is kept, may be irrecoverably lost. The 
result remaining is open to inspection, so long as it remains. 
The object sought, the why, or the function, is thus perma- 



. THE QUESTIONS OF INDUCTIVE LOGIC. 101 

nent, while the mode of producing the instrument ceases on 
the production of the machine. Thus watches are made by 
the use of very perfect machinery. No man can tell by 
looking at the watch how it was made ; for as soon as it was 
made, its connection with the machinery at' the manufactory 
ceases. Yet the adjustment of its parts continues, and at 
any time all we need, for the study of the relation of the 
wheels is present, and we can see why one wheel has just so 
many more cogs than that wheel into which it works. It is 
that one wheel may go round just twelve times as often as 
another. So as I examine a piece of elegant cabinet work, 
I cannot tell whether it was made by machinery or by hand. 
That is a point of history on which the article itself gives 
but little information. It carries, however, always with it 
the reason for the planning of its doors, and drawers, and 
slides, and pigeon-holes for papers. There are many things 
which might have been done in a dozen different ways, and 
only by some record of those present at the time can we 
know as a fact, in which of all the various possible ways it 
was actually done. But the reason for its doing is always 
there. No man can look at the Suspension Bridge at 
Niagara, and not know at a glance why it was built. 
Would any one ever guess, by looking at it, that the first 
cord that was thrown across was gotten over by tying it to 
a kite-string, after the kite had been flown over, and allowed 
to light on the other side ? And if the suggestion had come 
to them, that it might have been done in that way, by what 
process of logic could they now prove from the bridge, that 
as a fact, that was the method actually employed. It is 
thus evident that things themselves carry always with them 
the answer to the question, Why, but the answer to the ques- 
tion, How, is often either a matter of record, or by loss of 
records a matter absolutely unattainable.* 

* The importance of this line of thought is often overlooked. Thus 
it is specially true in geologic and natural history studies. For ex- 
9* * 



102 E VERY-DAY REASONING. 

If, now, there is such a question Why, there must always 
be a question Who, for the why is a question of mind 
wholly. Possibly there could be a What, and a How, and 
a Where, and a When, without any mind or thought, but 
there cannot possibly be a Why without mind and design. 
All effort to answer it is an endeavor to discover the mental 
conclusions or objects sought by him who planned it. Since, 
then, there is so much controversy about the admission of 
this question Why, and so much importance attaches to it, 
and so much, especially in relation to the question Who, 
which depends on it, the next section will contain a further 
discussion of it, under the aspect of the doctrine of Final 
Causes, or Design. 

FINAL CAUSES, 0E DESIGN. 

The expression, final causes, is one that has an important 
part in the history of philosophy, and therefore may not be 
lightly discarded. Its associations, however, are very apt to 
mislead us. Our notion of a cause is of something going 
before, and as an active force, bringing about the result we 
call its effect ; while final causes are not something going 

ample, it is the very smallest part of the problem to prove that the 
various species of animals might have been made through the pro- 
cess of the so-called natural selection. It has never been suggested 
that they could not have been created by an Almighty God. We 
have a professed record by the eye-witness and workman informing 
us that they were created. Thus the old question of the credibility 
and interpretation of the Bible is left exactly where it always has 
been, even after it is proved that it was possible to develop these by 
the method of selection. Suppose a case in court, where the prosecu- 
tion shows by hotel registers that the accused went from New York 
to St. Louis by way of Pittsburg, Crestline, and Indianapolis, would 
it overthrow this for his attorneys to prove that there was a route by 
way of Buffalo and Chicago, and another by way of Baltimore and 
Cincinnati ? No doubt he could have gone by that route, but did he ? 



FINAL CAUSES, OR DESIGN. 103 

before, but rather something to be brought to pass after- 
wards. The final cause is the object aimed at icAaking the 
preceding efforts. Thus, in military tactics, the ultimate 
triumph of the whole cause for which the general is fight- 
ing, is the final cause or object aimed at ; but under this, 
and subordinate to it, but promotive of it, each separate 
movement has its own immediate object or purpose, through 
which it is hoped to promote the other. So, in the erection 
of a monument, the final cause or object had in view is the 
tribute to the virtues of the dead, or a testimony in favor of 
some principle with which they were identified. In order, 
however, to the proper erection of that monument, it is 
necessary to rig a derrick and* build a scaffold. These are 
subordinate objects, having ultimate and final reference to 
the great end of all. So, between the thing done or the 
adjustment made and the end sought, there may be many 
intermediate results sought. Each of these is of the nature 
of a final cause in a lower degree, and differs radically from 
the antecedent efficient causes. 

Our conception of final causes will be made clearer by 
looking into the logical process by which the use of the term 
may be justified. This rationale of its us*e seems to be this. 
The result reached is brought about by the agency of the 
antecedent efficient causes. These causes were put in opera- 
tion by some mind. This intelligent agent was moved to 
put them into operation by some purpose ; so that, if we 
trace the chain of causation, we find it stated in this way : 
the result was produced by a cause ; that cause was set at 
work by some mind ; that mind was induced to its course by 
some purpose ; and, thus, that purpose is the final cause, 
beyond which we cannot go, or can at least only go by 
taking into our view some higher purpose or broader design. 
Take, for instance, the erection of a monument. The der- 
rick was erected to lift the stones to their places. The mar- 
ble shaft was lifted to its position by the horse-power at- 



104 EVERY-DAY REASONING. 

tached to the derrick. The derrick and machinery were 
built by tne mechanics. Team, machinery, and materials 
were managed by the workmen. The workmen were em- 
ployed and directed by the architect ; while he, in turn, is 
incited to carry out the purpose or design of those who em- 
ployed him. When, therefore, we begin to ask what was 
the cause of the causes, we are led back to the design of the 
mind where the plan originated. Design thus seems to be 
a clearer word for expressing the same thing which is meant 
by final causes. 

This doctrine of final causes, or design, thus divides itself 
up into three points, each of which will help us to under- 
stand the others and the whole subject. We have adjust- 
ments, functions, and purposes. Adjustments are made with 
a purpose in view. Functions are the uses of the matter or 
means empltyed. ^Purpose is the end to which the adjust- 
ments and functions tend. We have all three of these 
clearly distinguished in the erection of a house. The ad- 
justments are the architect's location of the flues. The 
functions are that one flue is for smoke, another for hot-air, 
and others for ventilation. The purpose is to have the house 
suitably warmed for the promotion of health. Therefore, 
the purpose answers to the question Why, the adjustment 
answers the question How, as it relates to the mind of the 
designer, and the function answers the question How, as it 
relates to the forces and laws of nature. The whole three — 
adjustment, function, and purpose — are manifest every- 
where, and when they are taken away, science is dispos- 
sessed of half its vitality, interest, and beauty. 

If, now, we contrast designs or purposes and efficient 
causes, we shall find them marked by four important points 
of difference. 

1. Purposes are in the mind alone, and so are subjec- 
tive ; while causes inhere in things or objects, and so are 
objective. 



FINAL CAUSES, OR DESIGN. 105 

2. Purposes attain their realization after the event, and 
so are subsequent ija time ; while causes are always antece- 
dent in time, and- are followed by their effects. 

3. Purposes are indicated by adjustment and function ; 
while causes are learned by observation and experiment. 

4. Man's purposes may utterly fail or be obstructed ; but 
the causes he sets in motion always act out their effect, re- 
gardless of consequences. 

Xo fact of every-day experience is more obvious than this 
last. The teacher before his class, with all kindness of de- 
sign, intends to exhibit to them some experiments, showing 
the action and power of natural elements. Unintentionally 
he brings two elements together, of whose explosive qualities 
he is ignorant, and then they do their work, and the dis- 
charge follows, precisely as if the explosion, with its man- 
gling of limbs and destruction of buildings, was what was 
intended. An American general conceives that a fortifica- 
tion could be demolished by exploding a large amount of 
powder near it. The thing was tried. An old boat was 
heavily loaded with giant powder, and thrust up close to the 
enemies' guns, and then discharged with admirable precision, 
and the hostile fort was not injured any more than if it had 
been struck by a ball from a pop-gun. The powder went 
just to the length of its efficiency, and neither wish nor pro- 
hibition could change it in the least. Nature's agents pay 
no attention to consequences. They give no heed to the 
wishes of those who furnished the active causes to the dor- 
mant, but inexorably work out their native result, and this 
even when they are counteract by some sufficiently pow- 
erful opposing agent ; for they then just go the length of 
their power, and stop. Thus, in such cases of counteraction, 
as in all others, they do their work. Our control over them 
is by measuring the force we first let loose, and by properly 
managing the antagonizing agencies. In both cases, how- 
ever, it is obvious that there is some design or purpose in 



106 E VERY-DAY REASONING. 

the first starting of the causes to action, as well as in the 
attempt to regulate the action by opposing agents. We 
never can get away from this end had in view, unless we 
utterly deny the existence of mind altogether. And, if we 
have this question Why, we cannot exclude the question 
Who, for a purpose implies a proposing mind. It will not 
do to limit this question Why to those things which we have 
seen done by persons, whose purpose we knew, for our in- 
duction has gone far beyond those cases. We have seen so 
much of the character of the work done by mind, with a 
purpose in view, and so much of the disorder of chance, 
where there is neither control nor plan, that the Methods of 
Agreement and Difference fully justify us in making the dis- 
tinction in those cases which are new to our observation. A 
young man may never have seen an electrical machine 
when he enters college, but it so bears the marks of adapta- 
tion to some design, that he will be anxious to ask what it 
is for, and how it does its work, and will be glad to know 
and admire him by whose ingenuity it was invented. His # 
information will be increased when he knows where it was 
first constructed, and when the success of the discovery was 
verified. The same is true in all investigations. We may 
not be able to get answers to all our questions, but the 
business of science is perpetually to strive after answers to 
the questions, What, How, Why, Who, When, Where, and 
fame awaits every discoverer of a new answer. 



PART FOURTH. 
STEPS IN INDUCTION. 

STATING THE QUESTION. 

IN all processes, some methods are better than others. It 
is always desirable that clear notions should be had of 
what we are attempting, and no time needlessly wasted. 
These remarks have a strong application to our reasoning 
processes. Very much time, and much valuable labor, are 
utterly wasted by foolish efforts to do useless things. We 
propose, therefore, to give some directions how we should 
proceed in this matter, in order to obtain the most reliable 
results in the least time. 

The first thing always to be done is to get a clear statement 
of the problem. Otherwise we are laboring at random, and 
if we accomplish anything, it will be rather by a happy 
chance than by any good effort on our part. To get this 
clear statement of the problem, there is often large knowledge 
needed. In the first place, it is important to know all that 
is already known on the subject. Otherwise, we may occupy 
our time in rediscovering what has already been found out. 
Many things have been independently discovered. Two 
workers have devoted themselves, at about the same time, 
to the same task, and both have reached the true result. 
More frequently, however, men have expended their strength 
in solving difficulties for which a solution had already been 
furnished, if they had only known it. Furthermore, cases 

107 



108 EVERY-DAY REASONING. 

occur where the supposed unsolved problem is only an 
unknown problem in appearance. Full knowledge of the 
whole subject would show that it was only an apparent dif- 
ficulty. Words are very often mistaken for things, and 
when we come to separate out what we know from what 
we do not know, and state our question in exact words, it 
resolves itself. In other cases, the distinct statement of the 
question brings such related knowledge forward to suggest 
the line of investigation, that the way is comparatively easy. 
No great discovery ordinarily is made all at once by one per- 
son. Generally,. some investigator starts the question. This 
sets all students in that department to thinking. Then one ' 
promulgates a theory, which further investigation over- 
throws. In it, however, "there may be a suggestion which 
some one else takes up, and although making but little pro- 
gress, still he adds something. It is a wide step from Watt's 
Steam-engine to the modern machinery of steam, and all this 
progress has been made by slow stages of success and fail- 
ure. So it has been everywhere. Great help, therefore, is 
secured by a definite statement of what is to be done, and 
keeping that constantly in view. 

Still further, the exact statement of the question will indi- 
cate clearly what is not known. It seems like a paradox to 
say, that before we are well prepared to undertake the solu- 
tion of some scientific question, we must not only know all 
that is known, but also all that is not known ; for how can 
we know what is not known, and if we know it, is not that 
enough. There is, however, a very important sense in which 
We may know just what is not known. We do know the 
measures and causes of many of the tides, but there are cer- 
tain irregularities whose existence is known, and their amount 
measured and tabulated, and the cause is not known. As 
another more familiar illustration, take the case of a young 
man who . proposes to write on the Saxon immigration to 
England. He first sits down and draws out a set of topics, 



STATING THE QUESTION. 109 

concerning which he already has certain facts, and concern- 
ing which there are other facts which he must know, and 
which he is sure he can get from history, and he notes these 
by asking the question, and leaves the answer to be supplied 
afterwards. Many questions of history are yet in that con- 
dition.- It is asserted by some that the original inhabitants 
of the British islands were cannibals. This others deny. 
The answer to that question is a specific question for study ; 
and where a point is thus stated, it gives great aid by point- 
ing out what methods are available, and what sources of in- 
formation we may apply to with the hope of obtaining deci- 
sive facts. This last is of great importance. Many facts are 
easily accessible, but they are of no value when* they are 
obtained. Other facts are decisive of the whole question. 
These last Bacon calls Prerogative Instances. They speak by 
authority and end controversy; and a clear statement of 
the question points out the direction in which we may look 
for such facts. Attention is thus directed to the facts which 
are significant. Previous to the occurrence of the total 
eclipse of 1869, which was visible in this country, scholars 
interested in the study of the sun and moon published very 
widely a list of questions, to which answers were requested 
from all who observed* that eclipse. By this means the at- 
tention of all was called to the things most noteworthy, and 
hundreds made observations on these points, without know- 
ing why they were so important. 

Another way by which the question may be definitely 
stated, and attention called to the significant points, is by 
the formation of good blanks. This is an extremely diffi- 
cult task. No person is competent to get up a blank who 
is not thoroughly familiar with the subject in all its bear- 
ings. Multitudes of blank's are issued, which are so indefi- 
nite in the inquiries they make, and so senseless in the points 
about which inquiry is made, that when they are filled up 
they are worth no more than mere waste paper. 
10 



110 EVERY-DAY REASONING. 

The following suggestions will aid in the construction of 
good blanks. The heads should be distinct* No one ques- 
tion or column should call for /in answer to more than one 
point. No two questions should cover the same point* It is 
out of character to ask, How many persons in a town cannot 
read and write? for some can read who cannot write* but 
probably none can write who cannot read* It would be 
proper to ask how many can neither read nor write. An 
examination of blanks will reveal endless violations of this 
rule. Mixed questions are extremely common* Another 
suggestion is, that the questions should call for short, defi- 
nite answers. Some questions, from their very form, cannot 
be answered either briefly or clearly. The reply must be a 
mere guess in any event, and then the reasons will modify 
the reliance to be placed on that estimate. Wherever it. is 
possible the answer should be called for in figures, and then 
exact measurement or numbering should be insisted on. 
Nothing is so valuable as exact numerical statements* Noth- 
ing reveals small concomitant variations so readily as tables 
of exact figures. In such tables, the point where the varia- 
tion begins can be easily detected, as also the point of its 
maximum and its termination* Under such circumstances 
the detection of its cause is made as easy as it is possible to 
make it. It will often, even in such cases, be extremely dif- 
ficult, but so far as help can be obtained from this direction, 
it will be thus secured. Another advantage derived from 
insisting on numerical replies is, that it excludes estimates, 
and requires measurement and enumeration wherever it is 
possible. But while by these means mere estimates and 
guess-work are excluded from portions of the blanks, it is 
not always best to leave them out of view altogether. Often 
there are matters wholly out of reach of measurement, which 
would, nevertheless, throw very much light on the whole 
matter. Space should, therefore, by all means, be left for 
such memoranda. They ought not to be included among 



GATHERING THE FACTS. Ill 

exact data, but kept separately, so that without bringing in 
confusion they may furnish suggestions. In calling for these 
additional matters the attention of observers should be di- 
rected to all indications and results that might have a mean- 
ing. In this way observation and experiment would be 
carried on under a system of topics, just as an author, in in- 
vestigating a subject preparatory to writing on it, finds it 
wise to map out the directions which his reading is to pur- 
sue. Of course it is important, finally, to call all the infor- 
mation, obtained by filling these blanks, to a common centre 
for comparison and compilation. 

GATHEEIM THE FACTS. 

The discussion of blanks above led directly to the impor- 
tance of gathering the facts on every subject of investigation. 
We sometimes hear of " dry statistics." Every such expres- 
sion is at total variance with every principle of scientific 
investigation. Statistics contain all the vital sap that is in 
any science, and nothing has just claim to the name of sci- 
ence which cannot vindicate its theories and laws by statis- 
tical data. The early progress of astronomy, as compared 
with other sciences, was due to the early gathering of its 
facts in tables of observations, so that when Kepler, Coper- 
nicus, and others came to the study, they had-at hand the 
memoranda of fulfilments and failures, by which the facts 
justified or contradicted the hypotheses of their predecessors. 
The testimony of Dr. Whewell to the vast importance of 
reliable statistical tables, in regard to the tides (see page 69), 
has already been quoted. What he there says on that sub- 
ject is just as pertinent to every other subject which may 
need investigation. Sir John Herschel, in his " Discourse on 
the Study of Natural Philosophy," speaks extendedly in be- 
half of this important matter of gathering facts, and calls 
attention to this point, that, while the work of analyzing 



112 EVERY-DAY REASONING. 

and explaining the facts, belonging, as that work does, to the 
higher and more difficult department of induction, requires 
the highest grade of scholarship and native genius, this 
work of gathering facts into tables, and collections of speci- 
mens, may be done by any and all who are willing to aid 
the progress of knowledge. He goes on to illustrate and 
enforce the remark thus : " What benefits has not geology 
reaped from the activity of industrious individuals, who, set- 
ting aside all theoretical views, have been content to exercise 
the useful and highly entertaining occupation of collecting 
specimens from the countries which they visit ? In short, 
there is no branch of science whatever in which, at least, if 
useful and sensible queries were distinctly proposed, an im- 
mense mass of valuable information might not be collected 
from those who, in their various lines of life, at home or 
abroad, stationary or in travel, would gladly avail them- 
selves of opportunities of being useful. Meteorology, one of 
the most complicated but useful branches of science, is at the 
same time one in which any person who will attend to plain 
rules, and bestow the necessary degree of attention, may do 
effectual service." Take this very subject of meteorology, 
which was so good a case in point in his day. In our own 
day we see it making rapid progress before our eyes, as it is 
furnished with the facts collected by extensive and system- 
atic observations carried on by the Weather Bureau of our 
own and other governments. When it was at first proposed 
to predict the coming of storms, long enough before their 
arrival to enable the shipping to d^much to avoid danger, 
or protect property from their violence, most persons heard 
the suggestion with incredulity. At present it is capable of 
proof, that these prognostications have saved, year by year, 
many times the cost of the whole department just in the 
single direction of ocean commerce. Such results never 
could have been attained without the numerous observations 
made and collated for study. As Sir John Herschel says, 



GATHERING THE FACTS. 113 

hundreds of persons can be employed to make these obser- 
vations who know but little of the science. A very few 
accomplished scholars are needed to direct the work, and 
study the results, while others can be employed to read in- 
struments, and make records from them, and do that work 
as well as the most scholarly. The departments of social 
science are now very much in the condition that this 
science of meteorology was then. Enough has been done 
to show that immensely more might be done, if only reliable 
statistics were accessible. These statistics, however, are not 
extant, and, until they are collected, very many of the so- 
cial theories cannot but be guesses, based on estimated sup- 
positions. Perhaps as severe a thing as ever was said in the 
British Parliament, was the assertion of a member in regard 
to one who had just delivered a speech full of statements 
and inferences from them, that " the gentleman draws on his 
imagination for his facts, and on his memory for his illus- 
trations." He was not the first, and it is to be regretted 
that he was not the last, man whose imagination furnished 
what should have come only from observation or informa- 
tion. From these sources (inaccurate and wholly imaginary 
facts) come, perhaps, more false conclusions than from false 
reasonings on real facts. 

While, therefore, no great amount of knowledge is need- 
ful for a good gatherer of facts, there are certain other 
things that are indispensable. And first among these is one 
which cannot be too much insisted on ; namely, absolute im- 
partiality in the acceptance and registration of all the facts. 
It seems a strange thing to say, but it is, if possible, a stranger 
thing to see that people have prejudices against classes of 
facts. They try to bend the facts to their own will, or else, 
deciding for themselves beforehand that certain classes of 
facts are of no value, they overlook and neglect them. 
Those who devote themselves to this work of collecting 
statistics or facts in any form should have no opinions. 
10* IT 



114 EVERY-DAY REASONING. 

Wooden men would be best, if they had brains enough to 
make records. So all devices to make instruments self-regis- 
tering are extremely important. Then a mere machine col- 
lects the facts, and there are no preconceived notions to 
interfere in the matter. Another equally important and 
closely related characteristic, that ought to be possessed, by 
statisticians, is scrupulous care in the separation of the facts 
from all inferences from them. It is a natural tendency of 
the human mind to draw these inferences from the facts 
before it. This is, indeed, the secret spring of all induction. 
One of our most common fallacies, therefore, is to confound 
the two, and treat an inferred fact as if it was an observed 
fact. The moment we step over from the plain facts to our 
inferences from them, we leave the office of the statistician 
and enter on the work of the philosopher, and so have no 
right whatever to include the results of our speculations 
among the facts furnished us by nature. These last all may 
rely on, but the former have no kind of claim to be put -in 
the same category. As a general principle, this will receive 
the assent of all. It is to be regretted that so few, especially 
of the young, who assent to it, will heed it as scrupulously 
as they ought. It seems an easy rule to follow, but in fact 
its observance is extremely difficult. Any one who has 
been much in courts will remember how many times they 
have seen honest witnesses, in their examination in chief, 
testify to the very points on which the case seemed to turn, 
and yet under the sifting process of cross-examination, when 
they were forced to distinguish carefully between what they 
knew of their own knowledge and what they had heard or 
inferred, it became evident to all, even to themselves, that 
their testimony was of very little account. Such people 
are sometimes accused of perjury. Their crime was prob- 
ably only stupidity. It was their business to tell the facts, 
and let the court and jury draw the inferences, but they 
proposed to do the work of all. This is both ridiculous and 



DETECTION OF LAW. 115 

wicked in 'such trials. It may not be so wicked, but it is 
ly as absurd, for one who proposes to furnish facts for 
scientific investigation to thrust his inferences in as reliable 
facts also. These inferences have their place, and a most 
important one it is, as we shall hereafter see, but it is of the 
first moment that the facts, when gathered as facts, should 
be kept separate from all else but facts, and then facts and 
inferences are ready for the service of all who would con- 
tribute to human knowledge. This gathering of all facts 
is, therefore, the next step after the clear statement of the 
problem. 

DETECTION OF LAW. 

This is the third and supreme step in the process of in- 
duction. All else is subordinate and preliminary to it. Even 
facts are of comparatively small value, except as they bear 
on this process by revealing, confirming, or overthrowing 
some law. This is, therefore, the legitimate place for infer- 
ences. The very achievement that distinguishes genius is its 
accomplishment of this work of drawing the correct infer- 
ence from the furnished facts. It may be, and perhaps is, 
impossible to tell just how the mind works, as to its subjec- 
tive operations, in doing this thing. Who will tell us how 
the mind thinks ? and this is a process of thought, or, better, 
one of the ways of thought. As to the process, so far as it . 
may be said to be objective, these induction^ or inferences 
are reached by these four methods of Agreement, Difference, 
Residues, and Concomitant Variations. As the attention is 
closely held to the array of facts* kept in view in the mem- 
ory, or otherwise offered for our consideration, agreements 
and differences and variations are seen or supposed ; and 
• then, pursuing these hints, the suggestion forms itself into an 
hypothesis, then is confirmed into a theory, and is finally 
verified into a law. We may now, therefore, distinguish 
these terms, for they mark the steps through which the 



116 EVERY-DAY REASONING. 

mind passes in discovering a law among submitted facts. 
There is first formed an hypothesis. This is a mere suppo- 
sition that would seem to explain 'a few facts which stand 
out prominently. No great value as yet attaches to it. Now, 
however, it is in a shape to be formulated into words, and 
then it will stand out more sharply defined for the consider- 
ation of the mind. As facts are now viewed in its light, 
they will range themselves into one of three classes, as they 
may seem to confirm or contradict the hypothesis, or have 
no bearing on the question. These last being set aside out 
of view, more study and attention will be given to those 
which do have a direct bearing on the subject. This further 
study may suggest new explanations of seemingly antago- 
nistic facts, by which they will confirm instead of contradict 
the supposition. This study may also suggest experiments, 
or special points or directions for observations, where some- 
thing decisive may be anticipated. As the investigation 
proceeds, the facts become so numerous which confirm the 
suggestion, that it is entitled to some measure of confidence. 
So far as there is a distinction recognized by writers in these 
two terms, it is that w T hen an hypothesis becomes thus some- 
what probable, but not established, it is a theory. Very 
often, however, these words are used without reference to 
any difference of meaning. Both are thus used as contra- 
distinguished from law, which is a theory established by all 
the facts. 

It is not often, however, that this first hypothesis suggest- 
ed to some patient student, maintains its position unchanged 
until it is acknowledged as an established law. More fre- 
quently, additional facts point out some modification that 
must be made, in order to accommodate the new facts which 
demand explanation. A not uncommon fallacy in inductive 
reasoning is to proceed after such a modification is made, 
assuming that the modified hypothesis will suit the facts 
already explained, as well as the original supposition. A 



DETECTION OF LAW. 117 

train-manager, in running a railroad, may not push an extra 
train up to another station to get it out of the way of those 
which follow, without also carefully reconsidering whether 
that will not thrust it into the road of those that are coming 
in the other direction. Every change necessitates an entire 
review of the location of all. So when, to suit some new 
fact, a theory is modified, the whole list of facts must be re- 
surveyed, lest that very modification makes it wholly incon- 
sistent with some fact with which it harmonized in its un- 
modified form. In doing this work of constructing and 
modifying theories to suit the facts given, it will be seen 
what extensive knowledge is required. It is mere blunder- 
ing to undertake to explain the intricacies of nature's opera- 
tions, without knowing very fully what the facts are in the 
case. Not only must the speculatist be familiar with that 
particular science in which his studies lie, but also knowledge 
of cognate sciences is almost equally important. Cicero's 
common bond not only subsists between all literature, but 
even more between all sciences, and he who is familiar with 
all will best understand the unsolved problems of any one 
of them. The spread of true astronomical theories gave a 
wonderful impulse to the study of mechanics ; and the de- 
velopment of the laws of mechanics in a marvellous manner 
aided the progress of astronomy. It is scarcely possible to 
pursue geology intelligently without very great familiarity 
with botany and comparative anatomy; and how can the 
problems of zoology be at all understood, or even approached, 
without a knowledge of fossil forms as well as of the living 
species ? It is just so everywhere ; so that, for the highest 
act of mind in induction, every sort of knowledge is of use, 
and extensive learning indispensable. 

Another faculty which is of vital importance in this work 
is a lively, vivid imagination, by which these facts given by 
this extensive knowledge can be clearly and steadily held 
before the mind. People are apt to think that imagination 



118 EVERY-DAY REASONING. 

is a faculty whose use is confined to the field of the orator, 
artist, and poet. It is, however, not less valuable to the 
student of nature. When Kepler undertook the study of 
the movements of the planets according to the Copernican 
theory, he saw at once that, if these planets moved around 
the sun, the orbit must have some form. He clearly stated 
the question when he asked himself what was the nature of 
that orbit in which they revolved. The facts were at hand, 
and his observations gave him- ready access to more facts as 
he needed them. He proposed, as his first hypothesis, that 
the orbit was a circle, and the sun was located in the centre. 
That was the simplest supposition. A very little comparison 
of the facts showed that this was incorrect. Abandoning 
that, he made another, which also proved incorrect. Pro- 
ceeding in this way, he made nineteen hypotheses in regard 
to the circular orbit and the place of the sun, every one of 
which the facts proved untrue, until he concluded that the 
orbit could not possibly be a circle at all. The next simplest 
figure that would seem to- offer any hope of being the right 
supposition was the ellipse. He then tried that, supposing 
that the sun was in its centre, when this also proved untrue* 
It was thus not until twenty false hypotheses had been imag- 
ined, adopted, and overthrown, that he made the right one, 
that the orbit was an ellipse, with the sun in one of the foci. 
When this was tested, it was found to meet all the require- 
ments, and is now a universally accepted law. He has not 
told us how many false ones he made, tested, and discarded, 
in his search for the rule that the squares of the periods 
are to each other as the cubes of the distances. But he has 
told us that he began with the simple numbers, with only a 
faint, vague hope that some proportion might be found to 
exist among them, and that he worked away with these until 
lie felt sure he must have exhausted every possible combina- 
tion. He then proceeded to a like consideration of the 
squares, until he had, as he supposed, tested every possible 



DETECTION OP LAW* 119 

combination of which they were capable. This was enough 
to have led any ordinary man to despair. Instead of aban- 
doning the project, however, he kept on imagining new pro- 
portions among the simple numbers and their squares, and 
the squares and the cubes. At last he hit upon the right 
proportion, and taking the three terms, he proceeded to find 
the fourth, hoping it would coincide with the term he had 
supposed. But, alas, he made a mistake in his computation, 
and threw it aside for some days. Still, the fact that it 
seemed to turn out more like a true proportion than the 
others led his mind back to it, and, as he said, as if guided 
by some good angel, he was led to go over the arithmetical 
calculation again, when, to his exquisite delight, he detected 
his mistake, and correcting this, beheld his fourth term un- 
folding itself as the true term he sought. This history is 
wonderful, as showing how near he was to losing all, just 
when at the point of discovery, and how his whole labor was 
stimulated by his vivid imagination, and made successful by 
his indefatigable patience. In this work of detecting the 
law amidst the facts gathered, the office of imagination 
is to hold up the possible new combinations of the facts, 
that the law may be seen through them. To the unimagina* 
tive mind, all facts are mere opaque quantities, showing 
nothing but what is on their surface. To the vivid imagina- 
tion of the scientific scholar, they are the transparent fluids 
in which float the great laws of the universe. It is, there- 
fore, of first importance, next to knowledge, that we should 
cultivate that faculty by which we can see things in new 
relations, and conceive the results that would follow the 
placing of them in these new conditions. These imagined 
hypotheses and theories are often wrong, but the ability to 
make them is indispensable to all discovery except that 
which comes by mere hap-hazard blundering. In every dis- 
covery reached by scientific processes, this work of the imagi- 
nation, conceiving and representing to the mind the possible 



120 EVERY-DAY REASONING. 

• 

explanations of the phenomena, is always first* After this 
hypothesis is thus furnished by the imagination, the next 
step is to test its truth* The method for this scientific veri-* 
fication will occupy the sections immediately following. 

VEEIPICATION. EXPLANATION OP FACTS, 

The difference between an hypothesis, a theory, and a law 
has been already explained. In narrating the experiences 
of Kepler in his discoveries to illustrate the use of the 
imagination in furnishing new hypotheses, the importance 
of this matter of verification was also exemplified ; for no 
sooner had he learned that some hypothesis he had formed 
was not correct, than he set his imagination to work, and 
developed a new one.' Immediately he proceeded to test 
this new hypothesis, as he had done the former ones, to see 
if it had any better foundation than they had. A most in* 
teresting and instructive history could be written on ex- 
ploded scientific hypotheses. It would be a valuable con- 
tribution to our knowledge, if we could find out just why 
each particular theory was abandoned as incorrect. In 
many cases it would be obvious just how it was shown to be 
manifestly untrue, and so given up even by its author. 
Many false theories, however, have had very able defenders, 
and the struggle between them and some true theory has 
been long, and sometimes fierce. To know just what points, 
and in what order, and why, the false theory had to give up, 
would be a clear illustration of the negative side of the sub- 
ject in hand. That negative side would throw great light 
on the positive side now under consideration. It is proposed 
to show what rules a true hypothesis must comply with, in 
order to justify our acceptance of it. In doing this, as large 
use will be made of the history of exploded hypotheses as 
possible for the sake of the contrast. 

It must, therefore, be noted at the outset, that no theory 



VERIFICATION. EXPLANATION OF FACTS. 121 

has any claims to confidence which cannot verify itself by 
some or all of these methods and rules. All truth is prov- 
able by some line of argument. Even the intuitive truths, 
which are perceived to be true as soon as they are under- 
stood, and true not only up to the limits of our experience, 
but in all time and all space, must, nevertheless, be equally 
justified by all facts, and so comply with all the tests for 
verification. It is not true, therefore, as is sometimes argued 
in opposition to the belief in intuitive truth, that it claims 
to override and disregard all experience. We do, indeed, 
and all men must, believe that everywhere Uxo and two are 
four, and all right angles are equal. These things, however, 
instead of overriding all experience, are in exact harmony 
with it. It is thus seen to be true by direct inspection, and 
this is confirmed by every fact bearing on the subject. 
While, however, some inductions, like our intuitions, are 
affirmed by all experience, there are others which are con- 
firmed by some facts, and apparently refuted by others. It 
is thus possible to have hypotheses in every varying stage 
of verification, from merest hypothetical guess or fancy up 
to the utmost certainty. Through all these stages almost 
every established law has come. Some have been hunted 
after, as if in darkness, until a flood of light broke in on the 
whole question by some brilliant thought of the patient stu- 
dent, and from that on, all investigation only added new T 
proofs to the same effect. Other discoveries, when they were 
first promulgated, had only a few facts in their favor, and 
many seemingly against them ; but step by step they won 
the ground, until the very facts that were urged as conclu- 
sive against them, were shown, when rightly understood, to 
be the strongest in their favor. 

The importance of this branch of the subject cannot be 
overestimated. If this verification is neglected, and we pro- 
ceed to act on our suppositions as if they were true, we shall 
fall into grievous, and often fatal error, and will deserve the 
11 



122 E VERY-DAY REASONING. 

disasters that befall us. Oftentimes, in every-day life, cir- 
cumstances will make thorough verification impracticable, 
but no excuse will apologize for the neglect of such verifica- 
tion as may be possible in the time and place. A military 
commander, judging from such facts as are within his knowl- 
edge, assumes that his enemy has retreated, and so neglects 
the usual precautions, when he is suddenly surprised and 
destroyed. If his conclusion was correct he could easily 
have verified it, by sending out a reconnoisance, and neg- 
lecting that, his whole course was an inexcusable blunder, 
due to bad logic in view of the facts. So there is great 
satisfaction to be derived from attaining conclusive proof of 
the correctness of our theories. Ail can remember how dif- 
ficult it was to get a sure way of proving our addition in 
arithmetic, but when we came to subtraction, the' addition 
of the remainder to the lower line should always give us the 
upper line ; and the multiplication of the divisor by the 
quotient always gave the dividend, as our proof in division. 
It is just such satisfaction and confidence w T hich is to be 
gained by a proper testing of our inductions. It is quite 
'possible* to arrive at the highest certainty. The notion that 
the planets revolve around the sun is directly contrary to 
our observation ; and yet what could we believe with more 
confidence than we do that truth of astronomy ? The belief 
in the criminal's guilt, when the evidence is wholly circum- 
stantial, is based on the indications found in the facts ; and 
yet so strong may those circumstances and facts be that no 
one has a shadow of doubt in the case. Thus this cumula- 
tive evidence becomes conclusive to every rational mind. 
When this point is reached we have what has heretofore 
been called a perfect enumeration. Imperfect enumeration 
was one of the fallacies named in the formal logics, but they 
gave no rules for avoiding it. They could offer illustrations, 
which could show how obvious it was in extreme cases, but 
no aid was given for testing, and the definition of a perfect 



RULE OF HARMONY. 123 

enumeration left the whole subject as obscure as before. A 
perfect enumeration was said to be one where the instances 
affirming the suggested law were sufficient to establish its 
truth. The all-important inquiry remained, as to how it 
could be told, where the instances were sufficiently numerous 
to do this. There are yet some matters, as will hereafter be 
seen, in regard to which the reasons for the rules do not ap- 
pear to be well settled. The rules themselves, however, will 
be recognized as those which receive the approval of men in 
their ordinary common-sense reasoning, and are of great 
value. This difficulty especially belongs to the Eule of 
Simplicity. II- is to be remarked, however, that the con- 
currence of two tests on either side are very much more 
than doubly as conclusive as one of them. It is like human 
testimony. If one man tells you a certain fact, you think 
it is probably true. If, then, another tells you essentially 
the same fact, in such manner as to exclude collusion, you 
are more than twice as certain as before, since it is extremely 
unlikely that two men should be independently moved to 
fabricate the same story. If, now, their statements are con-, 
firmed by a third independent witness, and no contradictory 
circumstance appears, there will be little doubt remaining 
as to its truth. So it is with these tests. The great conclu- 
sions of science are established by the coincident testimony 
of every Method of Induction, and every rule for verifying 
their correctness. These rules of verification will be now 
explained, and are five in number ; namely, The Eule of 
Harmony, of Simplicity, of Concurrence, of SUFFI- 
CIENCY, AND OF PREDICTION 

EULE OF HAEMOUT. 

A TRUE THEORY WILL HARMONIZE AND EXPLAIN ALL THE 
FACTS. 

This test is so familiar in all sorts of subjects, that but 
little explanation or illustration will be required. There 



124 EVERY-DAY REASONING. 

will not be much controversy as to the reliability of this 
rule. Its application is usually where this controversy be- 
gins. The most familiar example of the application of the 
test is in the criminal trials of the court-room. The argu- 
ments of the attorneys, as addressed to the jury, are almost 
all directed to that one point. The prosecution strives to 
show that the theory of the prisoner's guilt will explain all 
the facts elicited in the testimony; while the defence en- 
deavors to show that there are facts which the theory of his 
guilt will not explain. In all their previous efforts to secure 
testimony, they were hunting for facts bearing on that 
point. The one making as prominent as possible his theory, 
and the other opposing it ; both agreed that the true theory 
would explain every fact in the case. So in the history of 
science the same thing is true. In the conflict between 
Newton and his followers, in defence of the emission theory 
of light, and those who held to the wave theory, neither 
ever doubted that the truth must harmonize and explain 
every fact presented. And so Newton's theory of fits of easy 
.transmission was an effort on his part to account for the 
colors of thin plates, as they are seen in the colors of the 
soap-bubble and elsewhere. This was the most complex 
and intricate solution ever offered in behalf of the radiant 
theory of light as opposed to the wave theory. The false-" 
hoods told by children and criminals, when they are caught 
in doing wrong, are told under the pressure of the same 
instinct of reason. To explain their conduct they fabricate 
facts, which, if true, would justify their course, and so, 
although they lie, they admit their obligation to make the 
theory and the facts all harmonize. When Samuel, by 
divine authority, anointed Saul to be king over Israel, he 
ordered him to destroy the Amalekites utterly, even unto 
their herds and beasts of burden. When he met Saul on 
his return, he asked him if he had done as he had Jbeen 
commanded, and Saul said he had. Samuel instantly re- 



RULE OF HARMONY. 125 

plied, "What meaneth then this bleating of the sheep in 
mine ears, and this lowing of the oxen which I hear?" 
That fact was absolutely irreconcilable with the theory of 
his obedience, and at once convicted Saul of his falsehood, 
although he afterwards tried to get out of the difficulty. 
Excuses he could offer in abundance, but there was no reply 
to the inconsistency of the facts with the theory, and so God 
rejected him from being king. The whole art of deception 
in war proceeds on the same principle. Each general tries 
to conceal such facts as will reveal his true condition and 
designs to his adversary. Sometimes twice as many camp- 
fires are lighted as there is any use for, to make the army 
seem larger than it is ; v and again not half as many as are 
needed, in order to lure the enemy into battle. When 
Washington found himself in a position where he could 
march his army in view of the enemy, and then counter- 
march behind the hill, he kept the whole army marching in 
the circuit, until it had all gone two or three times over the 
visible space ; and so he gained time, because they thought 
they had seen three times as many men as he really had. 
In all these cases, as in every other, the rule is absolute, 
that the truth will harmonize and explain every fact affected 
by the case. 

The fundamental principle which underlies all this, is 
that which was laid down at the very outset in contrasting 
truth and falsehood. All truth is consistent and harmonious. 
Each truth is 'consistent with itself, and equally consistent 
with every other truth. We quote from the charge of Judge 
McLure on the trial of Jacobi for the murder of his wife in 
Allegheny County, Pa. "Truth is not only consistent with 
itself, but with all truth, while errors are not only at war 
with truth, but are always quarrelling and wrangling with 
each other." It is scarcely possible to imagine any false- 
hood which would not come in conflict with truth at some 
point. On the other hand, we are absolutely certain that 
11* 



126 EVERY-DAY REASONING. 

truth can be harmonized. We may not at once be able to 
see how it can be made consistent, but that is the effect of 
our ignorance, not the fault of truth. Further study of the 
facts already gathered, and especially further collection of 
facts by experiment and observation, will clear up the mys- 
tery. Just so far, however, as the facts seem to be incon- 
sistent with the theory, that theory is to be doubted. It 
may be true, but it certainly is not established. Before it 
can assert its right to men's belief, it must clear up every 
contradictory fact. 

The real source of error, however, is not either in denial 
or disregard of this rule, but in the admission of facts, and 
submission of the theory to the requirement that it should 
explain them. Enthusiasts in favor of a pet theory, like an 
over-zealous attorney, admit for consideration only such 
facts as the theory will explain, and insist on excluding all 
others from the view. Two or three remarks made in con- 
nection with the collection of facts are so important, and so 
relevant here, that they must be repeated. It is of the very 
first importance that there should be honesty in the accept- 
ance of all the facts. No apology can be made for the ex- 
clusion of any fact. To do so is to court deception and 
error. What is to be said of any study of man which 
leaves out of consideration his mental operations, his moral 
feelings, and social instincts ? Thus we have socialists, who, 
seeing that much of the evil which is in the world comes 
from efforts to get and to hold property, assert that all 
would be just right if all property was held in common ; 
and as jealousy and ill-will often spriug out of the marital 
relation, all these evils are to be cured by abolishing it, and 
making free-love universal. Their theories explain a few 
facts, and they exclude the rest. Others, seeing that drunk- 
enness and gluttony produce murder and disease, instantly 
propose to cure human ills by a system of diet and restraint. 
Darwinism would explain development by the survival of 



RULE OF HARMONY. 127 

the fittest in the midst of the conflict of life, and proves 
it by showing how individual members of a species have 
a struggle in the superabundance of their reproduction to 
gain food for all. If this was true, it is evident that the 
strong species, like lions and eagles, would be far more ene- 
mies of the weaker species, like lambs and quail, than the 
enemies of each other ; and so before the weakest of the lions 
and eagles would die by the strongest eating all the food, 
the whole breed of sheep and feeble birds would be utterly 
destroyed. Some modification of the theory of conflict of life 
is, therefore, indispensable. Huxley in his " Lay Sermons " 
alludes to this, when he says, " Any admissible hypothesis 
of progressive modification must be compatible with persist- 
ance without modification through indefinite periods." The 
most rudimentary and primordial forms of life are unques- 
tionably extant ; which Gould not be true if this conflict of 
life through scarcity of food existed. 

Another remark made in relation to the gathering of facts 
needs repetition here. The fact is to be taken just as it is, 
and not mixed up with any inferences. It is the fact that 
is to be explained, and not inferences from it. Many a fact 
is capable of an explanation, when somebody's inferences 
are inexplicable. This has been over and over again illus- 
trated in regard to the Scriptures,. Science has made some 
new discovery, and at once the cry is raised that this over- 
throws the truth of the Bible, because it contradicts it. A 
little closer and more honest study reveals the fact that it is 
not what the Bible says which is contradicted, but what 
was inferred from it. It was not the Bible that was upset, 
but the commentators. When it was asserted that the plan- 
ets moved round the sun, and not round the earth, the reply 
was that this was not true, because, if it was, Venus would 
show phases like the moon, and she did not. The assertion 
that she did not was only an inference, as if a man looking 
at a carriage, three miles distant, would say it was not 



128 EVERY-DAY REASONING. 

decked with flags. The flags may be there, but he cannot 
see them, and so it was with Venus's phases. The examina- 
tion of the fact must be so minute and particular, as to jus- 
tify negative evidence before its inconsistency with other 
truth is sufficient to overthrow them. In order to prove that 
a certain man was not in a given audience, it will not do to 
bring a witness to swear he did not see him, unless he can 
swear that the whole number was not over ten or twenty, 
and that it was impossible for him to have been there with- 
out his seeing him. So no scientific negation is justifiable 
until the investigation is complete, and excludes the likeli- 
hood of error. 

From what has now been said, an important question 
arises as to where the limit is to be placed in the admission 
of facts which any theory should be required to harmonize 
and explain. Surely every possible fact is not to be consid- 
ered in the verification of every theory. In investigating 
the wave theory of light, it is not necessary to inquire 
whether Thomas Young was an Englishman or not. His 
nativity has no bearing on the conclusiveness of his discov- 
eries and arguments on that subject. So there are, of course, 
multitudes of facts on other subjects than the one under con- 
sideration, whose explanation has nothing to do in the case, 
and, therefore, they need no consideration. The usual state- 
ment is to say that it must explain all related facts. The 
question, however, still remains as to what facts are related. 
The very object of legal rules, as to the admission of evidence, 
is to secure all related facts, and to exclude all others. No 
iron rule can be laid down by the mechanical and unin- 
telligent employment of which this point can be decided. 
Appeal must still be had to the general judgment of men, 
and that judgment is most likely to be brought out in an- 
swering the question, Ought the theory to explain a given 
fact ? Usually the relation between the two is so obvious, 
that the obligation of harmonizing them is a matter of 



RULE OF SIMPLICITY. 129 

almost direct perception. In other cases it is not so clear, 
but if there seems to be a relation, it will be the business of 
the defenders of a theory to show that there is no relation, 
and that, therefore, nothing can be argued in regard to that 
theory from that fact. In a criminal case, if the defence 
undertakes to exclude the proof of a fact, they must either 
show that the fact has no bearing on the case, or that the 
method of proving it is objectionable. The first point alone 
interests the scientific student, for as to the second he little 
cares how a thing is proved, so its truth is made certain to 
him. The great point is, what are the facts, and does the 
theory indicated by some or all of the methods) harmonize 
with and explain all the facts gathered which relate to the 
case in hand ? If the theory does so explain them, it has 
met and satisfied the first test of the truth of hypotheses, 
and that test by which false theories are most frequently 
overthrown. 

KULE OP SIMPLICITY. 

It is generally true that a false theory will not explain 
and harmonize all the facts, even when modified and changed. 
Some facts seem utterly to overthrow it, so that they make 
it wholly untenable. There are other cases, however, where 
there are two theories, both of which will give an explana- 
tion of the facts. What is to be done in such a case ? There 
is a very practical answer, on which men act as a rule. Take 

THAT THEORY WHICH OFFERS THE SIMPLEST AND CLEAREST 

explanation. This is especially employed by juries in the 
courts. Very few criminals fail to have some sort of an ex- 
planation of every fact furnished in the evidence. Their law- 
yer will go through the case, and often with great plausibility 
will try to show that all maybe understood by accepting the 
notion of his innocence; yet the jury and public opinion 
convict the man. They say there were too many things to 
explain away. The story was not straight enough. The 



130 EYERY-DAY REASONING. 

same thing is true in science. Take the Ptolemaic theory 
of astronomy. There was scarcely a motion of the heavenly 
bodies which it did not explain and account for by a system 
of epicycles. All it had to do with each new aberration 
was to add a new epicycle. When now the theory of Coper- 
nicus was proposed, it commended itself to scientific men, 
because it did away with all this complexity. Kepler enu- 
merates eleven motions of the Ptolemaic system, which are 
done away with by the Copernican system as wholly un- 
necessary. The best illustration, however, of this distinction 
between true and false theories, is found in the struggle be- 
tween the emission and the undulatory theory of light. This 
is probably the longest and most famous conflict in history, 
as it was a conflict wholly between scientists, and then be- 
tween those who agreed as to the methods of argument. 
The emission theory had for its supporters Newton, whose 
scientific authority was unequalled in his day, and others 
then and since of almost equal ability. That theory asserted 
that light was a substance emitted in rays from luminous 
bodies. This perfectly explained reflection, As for refrac- 
tion, it also had an answer, that the ray entering a denser 
medium was attracted downward by the increased quantity 
of matter. When it came to polarity, it added the notion of 
rays with sides. When it came to the colors of thin plates, 
it added the mystery of " fits " of easy transmission. When 
now the theory reached this complexity, with numerous 
other subordinate appendages required by other facts and 
experiments, the minds of scholars began to recoil from it, 
and insist that it could not be true, or it would not find such 
difficulty in explaining facts so simple. During Newton's 
lifetime, therefore, there were those who were seeking some 
other and simpler theory. In his day it was suggested that, 
instead of being material, a ray of light was simply the vi- 
bration of an extremely attenuated ether. This explains re- 
flection as well as rays, Refraction is due to one- edge of the 



RULE OF SIMPLICITY. 131 

wave striking the dense medium first, and so being retarded ; 
while the other edge goes on, and so its face is turned a little. 
Polarity is the reduction of all the vibrations to a single 
plane. The colors of thin plates are directly referable to 
the length of the waves, In all this there is no new hy- 
"pothesis demanded. But the best statement of the influence 
of this complexity of the one theory, and the simplicity of 
the other, on the question of their probability, is the follow- 
ing quotation from Whewell's "History of the Inductive 
Sciences," Vol. II., pages 107 and 108, Appleton's edition 
of 1870. 

" When we look at the history of the emission theory of 
light, we see exactly what we may consider as the natural 
course of things in the career of a false theory. Such a 
theory may, to a certain extent, explain the phenomena 
which it was at first contrived to meet ; but every new class 
of facts requires a new supposition — an addition to the ma- 
chinery*; and as observation goes on, these incoherent ap- 
pendages accumulate, till they overwhelm and upset the 
original framework. Such was the history of the hypothesis 
of solid epicycles ; such has been the history of the hypothesis 
of the material emission of light. In its simple form it ex- 
plained reflection and refraction ; but the colors of thin 
plates added to it the hypothesis of fits of easy transmission 
and reflection ; the phenomena of diffraction further invested 
the particles with complex hypothetical laws of attraction 
and repulsion ; polarization gave them sides ; double refrac- 
tion subjected them to peculiar forces emanating from the 
axes of crystals ; finally, dipolarization loaded them with 
the complex and unconnected contrivance of movable po- 
larization ; and even when all this had been assumed, addi- 
tional mechanism was wanting. There is here no unexpected 
success, no happy coincidence, no convergence of principles 
from remote quarters ; the philosopher builds the machine, 
but its parts do not fit; they hold together only while he 
presses them ; this is not the character of truth. 



132 EVERY-DAY REASONING. 

"In the undulatory theory, on the other hand, all tends 
to unity and simplicity. We explain reflection and refrac- 
tion by undulations ; when we come to thin plates the requi- 
site 'fits' are already involved in our fundamental hy- 
pothesis, for they are the length of an undulation; the 
phenomena of diffraction also require such intervals ; and 
the intervals thus required agree exactly with the others in 
magnitude, so that no new property is needed* Polarization 
for a moment checks us ; but not long ; for the direction of 
our vibrations is hitherto arbitrary — we allow polarization 
to decide it. Having done this for the sake of polarization, 
we find that it also answers an entirely different purpose, 
that of giving the law of double refraction. Truth may give 
rise to such a coincidence ; falsehood cannot. But the phe- 
nomena become more numerous, more various, more strange ; 
no matter — the Theory is equal to them all. It makes not 
a single new physical hypothesis ; but out of its original 
stock of principles it educes the counterpart of all that ob- 
servation shows. It accounts for, explains, simplifies, the 
most entangled cases ; corrects known laws and facts ; pre- 
dicts 'and discloses unknown ones ; becomes the guide of its 
former teacher, Observation ; and> enlightened by mechanical 
conceptions, acquires an insight which pierces through shape 
and color to force and cause*" 

If, now, we inquire why this rule is valid — why truth is 
thus simpLe and incomplex, it will be found to be a very dif- 
ficult question to answer. That it is so is the common ver- 
dict of mankind, and the testimony of all observation ; but 
there are many things we do not know, and most probably 
this is one of them as yet. It is to be remarked, however, 
that great stress is to be laid on the application of this rule, 
on the tendency of the theory to become more and more 
complex, with the increase of facts, and new phases of facts ; 
or its ability to maintain its simplicity without failing in its 
explanations. The study of the emission theory of light, in 



RULE OF SIMPLICITY. 133 

all the diversities of the suppositions it is compelled to 
make, as to the shape and character of its beams, will lead 
us to justify his expression, who called it a "mob of hy- 
potheses." Another illustration of the same increasing com- 
plexity of a false theory is found in the Cartesian doctrine 
of vortices, as an explanation of the mechanisnrof the heav- 
ens. Descartes suggested that matter was originally angu- 
lar, and that being thrown into a circular motion, it tended 
to separate into vortices, where the corners were rubbed off. 
Thus, the figure and general rotary motion was explained. 
The variation from the exact circle was accounted for by 
supposing thpse vortices to come in contact with each other, 
and so compress their curves at the point of contact. The 
comets were supposed to have the power of gliding into and 
out of these vortices, and so they were conceived of as flying 
through space in a serpentine course. Each star and sun 
was a centre-for a vortex, and the satellites moved in a vor- 
tex, of which their primary was the centre. As now the 
courses of the planets and satellites came to be closely ob- 
served, every new motion required some new addition to be 
made to the vortex, until the whole matter became involved 
in a universal vortex of confusion. 

Another illustration is found in the history of the Lin- 
nsean system of botany. This is an important illustration, 
as it is taken from the classificatory sciences, and shows the 
use of the inductive methods in those departments of study. 
A classification is artificial or scientific, as it finds its divisions 
running along distinctions found in nature or not. The 
scientific or natural division will bring together objects as 
nature has grouped them. An artificial classification will 
separate those which nature has obviously united. The 
great point, therefore, is to get the true basis of division, and 
make our distinctions on that ground. Linnseus took the 
sexual divisions of plants as his basis, and so made the 
number, position, and other characteristics of the stamens 
12 



134 EVERYDAY REASONING. 

and pistils of the flowers the method of distinction. For a 
while this was the almost universal mode of botanical study. 
The progress of the science, however, by and by came to 
show that on this basis of division plants which were evi- 
dently closely related were widely separated ; and others 
were brought together with nothing in common but the 
numbers of their stamens and pistils. To rectify these dif- 
ficulties more elements were introduced, and when it came 
to plants which had no true flowers, the employment of it 
was extremely difficult* Linnseus did not himself adhere 
to it in his classifications, because he found it required such 
complications to keep related plants together. When, now, 
after this Linnsean system had become almost universally 
accepted, the present system, called technically the Natural 
System, was proposed by the two Jussieus, uncle and nephew, 
of France. The fundamental basis of this classification was 
the character of the seed as to its lobes or cotyledons. Thus 
some are without cotyledons, others have one, and others 
two. That this is a true distinction, with its foundation in 
nature, seems probable, because the monocotyledons are 
endogenous, while the dicotyledons are exogenous ; that is, 
the former grow inward and by lengthening, as corn, while 
the latter add* rings to the outside, as the oak does. This 
last furnishes, in the physiology of the plant, a basis which 
seems to keep all the related plants together, while maintain- 
ing its simplicity. 

These illustrations of true and false hypotheses thus justify 
the rule ; so that, whether we see a reason for it or not, the 
fact is, that truth is more simple, consistent, and harmonious 
than error ; and its defenders find it a plainer path than the 
path of error. Perhaps no test receives more universal ac- 
ceptance, and more frequent application by unscholarly peo- 
ple, than this. In every-day life, in judging of the most 
trivial affairs, we hesitate about accepting any explanation, 
where explanations have to be further explained. We ex- 



RULE OF CONCURRENCE. 135 

pect truth to unfold itself, as we say naturally, that is with 
simplicity and directness. 

EULE OP CONOUKKENGE. 

Thus far, theories have been considered as hypotheses, sug- 
gested at first as obvious explanations of a limited number 
of facts, and pushing their way to general acceptance by 
their ability to explain every fact known, as connected with 
the subject, and this in a simple and natural manner. An- 
other thing which characterizes true inductions is now to be 
attended to. Often inductions are reached by starting at 
separate and apparently very widely separated clusters of 
facts ; or a conclusion is reached by considering one set of 
facts, and then leaving these and attending to another set of 
facts, we are suddenly delighted by finding ourselves brought 
to the sanfte conclusion. This is called the Consilience of 
Inductions by Dr. Whewell, in his work (now out of print) 
entitled, " The Philosophy of the Inductive Sciences." In 
his fourteenth aphorism concerning science, he states it thus : 
" The Consilience of Inductions takes place when an induc- 
tion from one class of facts coincides with an induction ob- 
tained from another different class. This Consilience is a 
test of the truth of the theory where it occurs/ 5 This con- 
currence or consilience of inductions had a very remarkable 
effect on the reception of Kepler's laws and Newton's theo- 
ries of gravitation. The questions to which Kepler ad- 
dressed himself were really those of mechanics involved in 
the composition and resolution of forces, and the motions 
resulting from them. Instead, however, of studying these 
abstract mathematical problems as abstract problems, he 
was studying them in the concrete case of the motions and 
directions of the heavenly bodies. It was easy to see, 
however, that if his theories were true at all, they were 
equally true of all motion and all force, anywhere and on 



136 EVERY-DAY REASONING. 

any scale. Here, then, was just the chance for this concur- 
rence of inductions. If the theories were true, the conclu- 
sions reached by studying the stars would also be reached 
by studying forces. As a fact, the two did go on hand in 
hand. From the time of Kepler onward, mathematicians 
made wonderful advancement in the science of mechanics, 
and as fast as that science progressed, its revelations threw 
new light on the suggestions of astronomy, and the discov- 
eries made by astronomers gave new directions to the stu- 
dents of mechanics. This was especially true after Newton's 
discovery of the law of gravitation. By that law there was 
given the other principal force with which the centrifugal 
force found in the planets, in their motion in their orbits, 
was compounded, and, of course, their curved motion was the 
resultant of these two forces. Indeed, Newton's discovery of 
this law was itself just such a concurrence of inductions. 
By the rapidity of falling bodies at the earth's surface, he 
had a basis for calculation as to what that rate would be at 
the distance of the moon. By the moon's monthly revolu- 
tion round the earth, and her distance from the earth, he 
had her rate of motion. By these two, sufficient mathemat- 
ical knowledge enabled 'him to calculate just how much the 
moon's course would diverge from a straight line or tangent. 
It was found that this divergence was not enough, if the 
moon moved round the earth in a circle, but that it was just 
what was required if it moved in an ellipse. But, further- 
more, even that first calculation did not come satisfactorily 
near the truth, as it showed that while the moon curved 
from this straight line or tangent so as to be thirteen feet 
from it at the end of one minute, yet, according to the sup- 
posed force of gravity, she should have been more than fif- 
teen feet from it in that length of time. Here the concur- 
rence was encouraging, but far from satisfactory. Not long 
after, a new calculation of the earth's radius was made in 
France, and it differed very much from what had been ac- 



RULE OF CONCURRENCE. 137 

cepted as true oefore, and, of course, used by Newton in his 
estimate of the earth's mass. The moon's distance is also 
calculated with the earth's radius as one of the given quan- 
tities, and a change in the radius would proportionally 
change the calculated distance. With these corrections, he 
went over his calculations again, and the result was found 
to agree with the phenomena to a remarkable degree of pre- 
cision. If, however, these concurrences gave great confidence 
in the induction thus reached, there was still another group 
of facts which might be investigated, and if the induction 
from them added another concurrence, the probability w T ould 
be very great indeed that the law was universal. This last 
group of facts was the course of the planets around the sun. 
The mathematical problem here was much more difficult, 
but Newton's transcendant mathematical talents enabled him 
to solve it, and its results confirmed fully the inductions from 
previous calculations. There was no hesitancy, then, in 
making the one further step, that as this law of the attrac- 
tion of matter directly as its mass, and inversely as the 
square of the distance, holds good on the earth, and between 
the earth and the moon, and between the sun and the plan- 
ets, it was a universal law of matter. To this same point 
all inductions, gathered in other ways from other facts, have 
pointed. 

In Tyndall's American lectures on light, he gave a most 
beautiful illustration of this concurrence of inductions. In 
explaining the presence of visible and invisible rays of light, 
he came upon the question of the proportionate amount of 
heat and light in a ray. By the use of the thermo-electric 
pile he was able to measure the amount of heat in the visible 
and invisible spectrum. In his statement of it he follows 
first Dr. WhewelPs method of means to get his data, and then 
represents them by curved lines. Thus he lets a straight line 
represent no heat at all so far as the ray is concerned. As 
soon as the pile begins to show itself affected by the heat, he 
12* 



138 E VERY-DAY REASONING. 

erects from the straight line a short perpendicular, at double 
the amount of heat a perpendicular twice as long, and so 
proportions the length to the amount of heat. Connecting 
the top of these perpendiculars he gets a curved line, which 
represents to the eye the degree of heat. Then making 
twelve such experiments most carefully, he compares them, 
and takes the mean curve of them all. From this it is dis- 
covered that the invisible or heat rays are about 7.7 times 
the other. He then gives another method of determin- 
ing the same thing. He first estimates the total emission 
from the electric lamp, and then by means of the iodine 
filter, determines the limit of the ultra red emission, and as 
the difference between these two will be the luminous emis- 
sion, it is found that the invisible is eight times that of the 
visible. " No two methods could be more opposed to each 
other, and hardly any two results could better harmonize/ ' 

This concurrence of inductions often manifests itself in 
another way, which, when it occurs, is a very strong confir- 
mation of its truth. It is not an unfrequent occurrence 
that empirical laws shall vindicate themselves by such fre- 
quent recurrence, that, although there may be no possible 
explanation of their regularity, yet much confidence may 
have grown up in their reliability. Thus even among the 
ancient Chaldeans the eclipses of the moon were known to 
come in a regular order of succession. The Copernican 
theory of the revolutions and the doctrine of gravitation 
explained why they should come in that order. So, also, 
Hipparchus detected and computed the amount of the pre- 
cession of the equinoxes. He could, however, give no 
reason for this slow retrograde motion. When, now, the 
theory of universal gravitation was discovered, it at once 
explained this phenomenon, by the unequal diameters of 
the earth, the amount of matter being greater under the 
equator, and this, owing to the obliquity of the plane of the 
equator to that of the ecliptic, kept drawing it over very 



RULE OF CONCURRENCE. 139 

slightly at each revolution. Thus in both tl ese last cases 
the true theory suddenly explained facts, which were not 
before supposed to be at all related. This is called the sub- 
sumption of apparently unrelated facts. When it occurs, it 
cannot fail to make a deep impression on the mind. Another 
instance of this same thing was in the sudden light thrown 
on the tides of the ocean by this theory of gravitation. It 
seems all plain to us now, but before the law was proposed 
and clearly developed, by what freak of imagination could 
it have been conceived that the same force that makes an 
apple or stone fall could make the tides rise up ? And yet 
when that doctrine of the universal attraction of matter was 
proposed, and the fluidity of the ocean taken into considera- 
tion, it not only made plain why there were tides at all, but 
it explained the difference of spring and neap tides, and 
morning and evening tides, and a very great variety of other 
variations. This sudden and unexpected explanation of ap- 
parently unrelated facts furnishes the propriety for Dr. 
WhewelFs word consilience, or jumping together of induc- 
tions. Here were phenomena on which the minds of phi- 
losophers were laboring, and all at once, as by a flash of 
light, the whole matter is made plain. Every test is satis- 
fied. Every fact is at once explained. The w r hole matter 
maintains the utmost simplicity. No new complexity is 
added, but a whole tangle of complexities is unravelled. 
There is a concurrence of inductions from the most varied 
directions. An experience of this same kind often occurs 
in the detection of crime and the conviction of criminals. 
At the outset all that seems certain is that there has been ' 
great villany. Who did it, or how it was done, no one 
knows. Some suggest one theory, and some another. The 
detectives are all baffled, and the lawyers are all at fault. 
Every fact, large or small, that can be gathered up has been 
carefully investigated. Theory after theory is tried, but 
some fact or other shows its impossibility. At length some 



140 E VERY-DAY REASONING. 

one makes the correct suggestion, and then it is marvellous 
how every fact points the same way. Things that seemed 
just to contradict each other are seen to be perfectly con- 
sistent, and, indeed, necessary to each other. % As new facts 
are brought to light, they only serve to confirm what is 
already known. As in science, so here : things that did not 
seem to have any bearing on the subject, or connection with 
it, now evidently are part of the same chain of events, and 
a common interdependence is manifest all through. 

In this connection it is important to note how hypotheses 
clear up exceptional cases. It is often said that exceptions 
prove the rule. Nowhere is this more true, or true in a 
more obvious sense, than in the history of science. The 
secret of this is that the true hypothesis reveals the causal 
reason, why there should be such an apparent exception ; 
which, instead of being a real exception, is a preeminent 
instance of conformity to the rule. The most remarkable 
instance of these exceptions, coming up to confirm a law, is 
in the case of the discovery of the cause of what are known 
as the Secular Inequalities of the motions of the members of 
the solar system. Thus it was long known that the moon's 
motion in her orbit was slowly accelerating ; that is, the 
rate is a little faster than it has been heretofore. A similar 
acceleration is going on in the case of Jupiter's mean mo- 
tion, but there is a retardation in the case of Saturn. Here 
was something that seemed wholly exceptional. In the first 
place it looked like an anomaly that there should be any 
variation from year to year, and an indefinite number of 
hypotheses were suggested to account for it. But in 1787 
La Place discovered that this acceleration of the moon's 
mean motion was due to the influence of the sun's attrac- 
tion on itj and that, after a very long period of time, that 
action would be converted into a retardation ; and that 
in the case of Jupiter and Saturn, it was due to the mutual 
attraction of the two planets on each other ; and further, 



RULE OF SUFFICIENCY. 141 

that while now the effect of this action was to retard Saturn 
and accelerate Jupiter, in course of time it would also be in 
that case so changed that Jupiter would be retarded and 
Saturn accelerated. So accurate was this last calculation 
that he fixed the length of time during which one planet is 
retarded and the other accelerated. That period is nine 
hundred and twenty-nine years and a half. In speaking of 
this apparent exception, La Place says : " And thus the lot 
of this great discovery of gravitation is no less than this, 
that every apparent exception becomes a proof — every 
difficulty a new occasion of triumph. And such is the char- 
acter of a true theory — of a real representation of nature." 
This, then, is the nature of the test of the Concurrence of 
Inductions. The same conclusion is reached by reason- 
ings from different sets of facts. Phenomena, hitherto 
not supposed to be related, are shown to be explicable on the 
same principles, and thus their correlation is discovered. Ex- 
ceptional cases, hitherto seemingly contradictory, are shown 
to be consistent, and, instead of controverting the law, are its 
most conclusive proofs. This test may not always be found 
applicable. There may occur cases when it does not come 
m the way of a true theory to be confirmed by these happy 
concurrences. When, however, a theory is thus confirmed, 
it is among the strongest proofs of its correctness. 

EULE OP SUFFICIENCY. 

In speaking of the difference between final and efficient 
causes, attention was called to the fact that nature's forces, 
when once let loose, always did their work, whether in our 
plan the results brought about were all included or not. If 
the causes are put in operation, the effects appropriate 
thereto will be brought about, w T hether we intend them or 
fear them. Even if they should be precisely the reverse 
of what we want, still causes and forces pay no attention to 



142 EVERY-DAY REASONING. 

our desires, but, as we might say, blindly work out their 
result. Now this fact of the inevitable accomplishment of 
all their proper results by causes, furnishes us a means of 
testing the correctness of our inductions as to the causes in 
any particular case. If, for example, our induction leads 
us to assign a cause, and the necessary results of that cause 
are not present, then we may be reasonably sure that our 
hypothesis is not correct. If all the results that ought to be 
produced by its presence are found to be on hand, then 
there is great probability that our theory of the case is true. 
It will thus appear that while facts require theories to ex- 
plain them, theories also require facts to bear them out. 
Hence our test of the Sufficiency of the Facts. Theories thus 
at times demand new facts never before observed. Allusion 
has already been made to the objection raised to the Coper- 
nican theory of astronomy, from the absence of phases in 
the planet Venus. It was correctly argued that if Venus 
revolved round the sun, she should show phases like the 
moon, so that there should be a quarter Venus and full 
Venus, as there is a quarter moon and a full moon. When, 
now, Galileo succeeded in constructing a telescope sufficiently 
powerful, he beheld Venus showing phases exactly like the 
moon. Thus a fact demanded by the theory was forthcom- 
ing when men were enabled to observe it. So when the 
theory of universal gravitation was proposed, it was at once 
seen that if true certain other things would also be true, 
which had never been observed before; namely, that the 
motions of the heavenly bodies, instead of being in right 
lines across the face of the firmanent, should be in waving 
tracks, as drawn and released by this force. So when they 
perfected their astronomical instruments to such a degree, 
that variations so slight, as they must appear to us, could 
be detected, it was found that they did not move in right 
lines, as they seemed to do to the naked eye, but that there 
was just the waving motion demanded by the theory. The 



RULE OF SUFFICIENCY. 143 

last planet of the solar system was discovered just in that 
way. It was supposed for many years that Uranus was the 
outermost planet of our system, but observations of the 
course of that planet failed to satisfy the calculations to the 
requisite degree of exactness. The only way to explain 
these aberrations was to suppose that there existed another 
planet exterior to Uranus. No one knew that he had ever 
seen such a planet. It had, indeed, been before seen, but 
was supposed to be a comet, and as it changed its place it 
was lost sight of. About the years 1843-6, the variation of 
Uranus became so great that, taking its amount and direc- 
tion, there were furnished sufficient data to solve the prob- 
lem of its location. It is well known that this difficult 
mathematical calculation was successfully performed by Le 
Verrier, a Frenchman, and Adams, an Englishman, and 
that the planet Neptune was discovered by Galle, at the 
Berlin Observatory, September 28, 1846, in the exact spot 
fixed by their calculations, It is scarcely possible to con- 
ceive a stronger proof of the theory than was thus given in 
its pointing out a fact before it was observed. 

An equally instructive discovery was made in the science 
of optics very much in the same manner* The phenomenon 
of polarization had, by the undulatory theory of light, sug- 
gested that at four special points at the surface of the ether 
wave in double-refracting crystals, the ray was divided, not 
into two parts, but into an infinite number of parts, forming 
at these points a continuous conical envelope, instead of two 
images. This was the conclusion arrived at by Sir William 
Hamilton, of Dublin, a profound mathematician, who based 
his calculations on the results reached by Fresnel, a French- 
man. No eye had ever seen such an envelope. There was 
no evidence of its existence except that, if the theory was 
true, such a thing should exist. Mr. Hamilton requested a 
friend of his, Dr. Lloyd, to try it and see. This he did with 
the utmost care. He took a crystal of arragonite, and cut it 



144 EVERY-DAY REASONING* 

just where the theory said it ought to be cut) and fixed it 
just as the theory said it should be mounted for observation, 
and looked jus: where the theory said the envelope should 
be seen". And there it was. The fact called for by the theory 
was found just in the right place. 

This test of the sufficiency of the facts is often of the 
greatest importance in legal trials. It very rarely happens 
that an innocent person can be convicted, and every fact de- 
manded by the theory of his guilt be found forthcoming. 
So, in the case cf a criminal, it very rarely happens that any 
important fact made necessary by the theory of the prosecu- 
tion is wanting, and every fact demanded by the defence is 
present. This is especially true where a prisoner sets up a 
false alibi. Sometimes the prosecution is unable to get a 
case strong enough to require the defence to set up any 
theory at all. The case breaks down by its own weakness 
and inconsistency. But whenever the prosecution so gath- 
ers the web of evidence around him that a reasonable man 
would say : " Well, he may be innocent, but it begins to look 
very much as if he was guilty," it becomes important for 
him to advance such a theory of the facts, which he does 
not deny, as will harmonize them with his innocence. In 
such a case, he too must submit to the test of the sufficiency 
of the facts. This test was conspicuously applied in the case 
of Jacobi, already alluded to. His defence was, that the 
body found in the woods, so decomposed that it could not be 
recognized, was not the body of his wife. In charging the 
jury, it was ruled that, if it was not the body of Mrs. Ja- 
cobi, then she must be somewhere else, and no attempt had 
been made to account for her absence, which had awakened 
so much alarm in the community. As a still further fact 
called for by the theory of the defence, some other woman 
must have been lost about the same time. The state of de- 
composition in which the body was, fixed the time at about 
the time Mrs. Jacobi disappeared. No other woman had 



BtJLE OF SUFFICIENCY. 145 

disappeared from that neighborhood about that time, and it 
was hardly possible for any one to have done so without ex- 
citing the same concern that had been manifested in regard 
to the fate of Mrs. Jacobi. Here were facts called for by 
the theory of the defence which were not found, and their 
absence made very seriously against the theory. 

The most recent illustration of this test in the department 
of science, is in regard to the doctrine of the development 
of all animal life, man included, from an original life-form. 
If this is true, then obviously these steps ought to be appar- 
ent and ready for comparison. But the step between man 
and the highest extant animal yet known is so large, that it 
is conceded that no variation is sufficient to account for it. 
Here, then, is a fact called for by the theory, namely, an 
intermediate species between man and the ape and monkey. 
This has been recognized by the advocates of the theory of 
development, and so they have .supposed the existence of an 
anthropoid ape. For this the fnost active search is now 
going on. The discovery of such an animal will hardly be 
conclusive in favor of the theory, in the absence of any 
variation whatever in present species, for the existence of 
species is one of those cases where the causes that produced 
them have ceased for the present to act, and only the results 
remain. It is hard to tell, by looking at a building after the 
workmen have left it, who built it, or how the great orna- 
mental stones on its cornice were lifted there. It is, how- 
ever, manifest that the absence of that anthropoid ape is 
fatal to the theory. It will hardly do for him to be a fossil 
ape. His place in the scale shows that he must have been a 
recent, indeed, except man, the most recent species in the 
list; and when jelly-fishes and other rudimentary forms 
have been able to survive amidst the devastation of stronger 
forms of animal life, surely he ought to have been able to 
hold his owjn, at least until his next successor should have 
seen his face. 

13 K 



146 EVERY- DAY REASONING. 

The famous dogma in regard to falling bodies, put forth 
with authority by Aristotle, is a case where a fact demanded 
by his theory failing to be fulfilled, but just reversed, utterly 
overthrew the theory. Aristotle asserts positively that the 
rapidity of the fall of bodies is directly in proportion to 
their weight. If this is true, then a body ten times the 
weight of another, will fall ten times as fast. Aristotle 
says it will. As a fact, it has always been found that it 
will not. 

The fundamental principle on which this test is based, is 
the symmetry and completeness of truth, or, which is for 
this purpose the same thing, the completeness of nature's 
action. Nature never overlooks or forgets anything. All 
consequences and results are fully carried out in every direc- 
tion. This legitimates the second of Whewell's two great 
questions of inductions. On the proposal of any hypothesis, 
the first question is, " Why not ? " By this, attention is im- 
mediately called to any fact already known which would 
make the proposed hypothesis inadmissible. This is the 
question which more directly calls out the application of the 
three former tests. If the gathered facts require an in- 
creased complexity for a possible explanation of all the 
facts, and there are no concurrences by which it appears 
that the supposition named would correlate and unify the 
unrelated facts and exceptions, then there is a reason why 
not. But suppose no such reason why not appears, the next 
step is the application of this test of sufficiency in answer to 
the question, " What then ? " If the theory is true, it will 
draw along with it certain other conclusions which must 
also be true, and their existence or absence is one of the 
best tests of its truth. True inductions thus become the 
pilots of investigation. They direct observation and experi- 
ment. These directions or demands for new facts are some- 
times called deductions. It is certain that they may be 
thrown into the form of syllogisms, -with the hypothesis as 



RULE OF SUFFICIENCY. 147 

the universal premise, and the suggested experiment as a 
case under it, with the conclusion as the demanded fact. 
Thus, for illustration, the deductive reasoning in the case of 
the discovery of Neptune ran in this way : 

The divergence of the planets from their true orbit is due 
to attraction by some other body of matter. 

Uranus is diverging from its true orbit There must be 
gome exterior planet to attract it. 

This deductive process always follows any great inductive 
discovery, and is itself one of the most fruitful sources of 
further discovery. When these further discoveries are made, 
they again become the universal premises for yet other de- 
ductions. The history of the application of scientific knowl- 
edge to the uses of man is full of such correct deductions in 
answer to this question, What then? The lightning-rod was 
a direct deduction from Franklin's identification of light- 
ning and electricity. The telegraph was suggested as a de- 
duction from the ability to magnetize soft iron by passing a 
current through a wire coiled round it, while the iron lost 
its magnetism as soon as the current was cut off. The art 
of photography was a deduction from the discovery of the 
chemical effect of light in fixing colors. The mariner's com- 
pass was a deduction from the discovery of the fact that the 
magnetic needle pointed always to the pole star. The num- 
ber of such deductions, which have furnished the suggestions 
for new adaptations of scientific truths to the practical affairs 
of life, is almost beyond computation. The question, " What 
then ? " may not have been consciously before the mind of 
the inventor, but he was following out .the scientific truth 
to the facts, which must come true, if it is true ; and their 
coming true is a strong confirmation of the correctness of 
that scientific theory on which his deductions were based. 



148 EVERY-DAY REASONING. 

fiULE OF PKEDICTION. 

This test of Prediction is universally recognized as the 
final, surest, crucial test. Every writer on the subject as- 
signs it this place. No matter what school of metaphysics 
he belongs to, or w 7 hat department of science he adopts as 
his specialty, every one agrees that the ability to predict 
what will follow under certain circumstances, is not only the 
test of the correctness of the scientific theories involved, but 
also of the familiarity of any speaker with the subject in 
hand. It is thus not only the test recognized by science, but 
it is equally the test approved by common sense, and em- 
ployed by common people in their every-day reasoning. 
When they discuss the ability of a business man, they offer 
as the proof of his business capacity, that he advised them 
on a certain occasion to buy certain articles of merchandise, 
as he thought the price would rise. They bought as ad- 
vised, and made largely because of the advance in prices 
that followed. Under his advice they afterwards sold out, 
and prices went down as he had warned them they would. 
Of another they say, he is singularly unfortunate in never 
buying right, or selling right, or in giving others advice 
So we judge of physicians. He who can tell us the course 
of disease, and the effect of medicine, and can select remedies 
which will relieve si&kness, is consulted and trusted. Every 
branch of business, and every department of the professions, 
offer examples confirmatory of this same principle. 

The same thing holds good in science. In chemistry the 
correctness of our inductions, as to the powers and natures 
of the various elements, is tested by the ability to tell be- 
forehand what result will follow their mixture in different 
proportions. It is asserted that' the explosions that occur 
with refined petroleum come from the neglect to subject it to 
sufficient heat, so that the light gases should be driven off. 
Therefore, when in burning it in a lamp, the oil gets so 



ItULE OF PREDICTION. 119 

heated as to begin to give off this light gas, it mixes with 
the air, and when the proper proportion is reached an explo- 
sion follows. To test this some poor oil is tried, and, al- 
though it looks all right, when it is heated to 100 or 120 
degrees Fahrenheit, and a burning taper is brought near its 
surface, it flashes or explodes with the gas. That is just 
what was predicted, but, being in an open vessel, only a 
little gas collects, and no danger is to be feared in the 
experiment when properly made. It is asserted that nothing 
of that kind will occur with properly refined oil. The thing 
is tried, and when the oil is heated to 120 or 125 degrees, 
the burning taper is thrust down into the oil until it is ex- 
tinguished as if it had been in water. The prediction is 
again fulfilled. 

A conspicuous instance of the popular confidence in this 
test is found in the reception with which the prognostications 
of the present head of the Weather Bureau have been re- 
ceived. Similar attempts to predict the weather had been 
made by almanac makers long ago, and had received almost 
no consideration, or rather had been met with ridicule, just 
because it was a rare thing for them to come anywnere near 
the truth. Besides this utter failure of the almanac makers, 
almost every one had been pressed by business or pleasure, 
to try his own hand at guessing whether it would rain or 
not, as he planned his farm labor, his journeys, or his busi- 
ness. The result of all this was that to call a thing as un- 
certain as the wind and weather, was to express the most 
utter want of faith in any assertions about its future course. 
When, then, Gen. Meyer began publishing his Probabilities 
of the weather, few expected them to be of any great value, 
and very many looked upon the whole thing as a useless 
waste of the public money. Very shortly, however, it came 
to be a common matter of surprise how exactly these prob- 
abilities came true. More experience still further confirmed 
their correctness, until now no one, whether scientist or lay- 
13* 



150 EVERY-DAY REASONING. 

man, who has paid any attention to the matter, doubts that 
great progress has been made in this matter of meteorology, 
and that the present head of the Weather Bureau has hit 
upon many of the true principles on which it is based. 
That universal confidence with which it is now regarded, is 
the result of the success of its predictions ; over eighty per 
cent, of which have been verified, so far as they related to 
New England and the Atlantic States, with a decreasing per- 
centage as you go* westward ; since the storms and changes 
progress eastwardly in the main, thus giving more facts 
from which to gather the eastern predictions than can be 
obtained for the western. ^Yet even for the Pacific States 
more than fifty per cent, are verified. With such a fulfil- 
ment of the predictions, no one can doubt bufc that at least 
some of the main principles have, indeed, been discovered. 

The following interesting fact will show how the leading 
scientific scholars regard this test of prediction. In 1871, 
an expedition was fitted out for the purpose of investigating 
matters relating to natural history, and especially zool- 
ogy, by deep-sea dredgings in the South Seas. That expe- 
dition was placed under the direction of Professor Louis 
Agassiz, who, in the department of zoology, had in his 
day no superior. Before he set out he addressed a letter, 
through the papers, to Professor Pierce, of the Coast Survey, 
giving a detailed statement of the kinds of animals he ex- 
pected to find in these deep-sea dredgings in that part of 
the ocean. In assigning his reasons for this letter, he puts 
it explicitly on the ground that if zoology is entitled to the 
rank of a science, it must vindicate its title thereto, by show- 
ing its ability to tell beforehand what will be found as the 
result of its investigations. He declared his belief that it 
had reached that stage of progress at which it was able to 
substantiate its claims by that final and surest test. In 
order, therefore, to show this, he, in that public way, before 
he started, recorded what he expected to find ; so that if the 



RULE OF PREDICTION. 151 

expedition was successful, it would not be left to him to say 
whether he found what he expected or not. What he ex- 
pected was recorded in that letter, and everybody could see 
for themselves, when he got back, whether he found what he 
was looking for. In his letter he alluded to what he feared, 
and what actually occurred, either that he himself should 
die, and so his predictions be lost before they were verified, 
or that the expedition should fail, and so its verification be 
postponed for a long time. The expedition did fail at least 
in the main. No such success was had as to settle the ques- 
tion of the correctness of his expectations. The eminent 
professor has since died ; but in that letter there is left on 
record his predictions. Now whether, when those deep-sea 
dredgings come to be made, as they most undoubtedly will 
some day, they will meet his predictions or not, is not for 
our immediate purpose an important question. In any event, 
his writing that letter for the purposes named in it, and the 
universal acceptance accorded to it by all classes, settle as 
beyond all controversy his belief (and the agreement of all 
others with him in the belief) that this test of prediction 
was the most reliable and conclusive of all the tests of in- 
ductive knowledge. 

The fundamental principle on which this test is based, is 
the uniformity and regularity of Nature's laws and forces. 
The principle on which the test of sufficiency is based also has 
application here. Nature not only is reliable for its uniform- 
ity of action, but also for leaving nothing omitted or neglect- 
ed. Every cause works itself out in every case in the same 
way, under the same conditions. If, then, we have reached 
a correct knowledge of the nature and power of these causes, 
we can tell what effect they will produce when we bring 
them together in our experiments, or find them coming to- 
gether in our observations of nature. This test is closely 
allied to .recombination as a test of analysis. It is the syn- 
thesis of the forces we have theoretically analyzed in our 



152 EVERY-DAY REASONING. 

investigations. If our decomposition has been correct and 
exhaustive, we must be able to tell what results shall follow 
the recombination of the elements so found, and until we 
are able by this recombination to fulfil our predictions, 
based on our analysis, we are not justified in claiming that 
our analysis is exhaustive as to quantity, quality, and rela- 
tion. So it is in our knowledge of caused truth of every 
sort. We can rely on the same causes bringing out the same 
results in every case where the conditions are the same. 
When we are right, therefore, in our inductions, they give 
us a sure basis for our predictions. 

The science of astronomy has furnished many of our best 
illustrations, and it will again admirably serve us. Shortly 
after the announcement of Newton's theory of universal 
gravitation, the eminent English mathematician and astron- 
omer undertook its application to that interesting class of 
heavenly bodies, the comets. Such investigations as he was 
able to make enabled him shortly to predict the appearance 
of a comet in 1758 or 1759, and the question of its return 
at that time was looked forward to with the utmost interest. 
In his calculations he had seen the presence of that problem 
of extremest difficulty, as to the effect of the attractions of 
the planets upon a comet. He announced the problem, but 
did not undertake to solve it, and so did not undertake to 
fix the date more definitely than 1758 or 1759. Before, 
however, the comet appeared, Bailly, assisted by Lalande 
and a female mathematician, Madame Lepante, undertook 
the problem, and fixed the time of its arrival at its perihe- 
lion as likely to be about April 13th, 1759 ; saying that it 
might vary from that a month or so, as, owing to the near 
approach of the time and the difficulty of the calculation, 
they could not fix it more exactly, and yet have it published 
in time to be a true prediction. This haste in its publica- 
tion showed, as scarcely anything else could, the importance 
they attached to prediction as a test of truth, just as the ap- 



RULE OF PREDICTION. 153 

pearance of the comet at its perihelion, on the 13th of March, 
1759, proved, as nothing else could, the truth of the theory, 
and that the attraction of the planets had hastened its re- 
turn even more than had been expected. This comet has 
ever since borne Halley's name, in honor of him who had 
first secured for the doctrine of gravitation the confirmation 
of prediction. To what exactness that power of astronomi- 
cal prediction has since been brought, will be best illustrated 
by those wonderful scenes in the heavens, the eclipses. Some 
years ago, astronomers had announced a most remarkable 
total eclipse of the sun, which would be best seen in Siam. 
It was specially remarkable and valuable on account of the 
duration of the period of total obscuration. Generally, 
eclipses of the sun are not total for more than one or two 
minutes. This was total. about seven minutes. Most civil- 
ized nations fitted* out expeditions of scientific men for its 
observation. The French, whose influence is dominant in 
Siam, sent out a specially complete expedition. The then 
reigning king of Siam had been taught in his youth our sys- 
tem of mathematics, and having a natural fondness and 
capacity for such studies, had pursued them until he was 
able to make out his own calculation of its duration and 
times. Here now, he saw, was the chance to test European 
science with his. own, and he determined to leave nothing 
undone to make the test thorough. According to the notions 
of the scholars of his own country, predicting an eclipse was 
utterly absurd. He, therefore, selected the best location to 
be had, right in the path of the total shadow, and procured 
the most perfect instruments to be bought, for watching the 
sun at the appointed time, to see what was the truth in the 
matter. Most of his noblemen opposed him, while the mass 
of the people were shocked by the suggestion. Everybody, 
however, was intensely interested. When now the eclipse 
came, exactly as predicted by the calculations, and more 
nearly on the time of his calculations than of any others 



154 EVERY-DAY REASONING. 

published, the case was settled. The king's death, not long 
after, from malarial disease contracted where he was watch- 
ing that eclipse, is by many believed to be partly attribu- 
table to the extreme mental excitement beforehand, and the 
shock that came with the result. Certain it is, that from 
thence began a day of most rapid revolution in the domestic 
affairs of that country. The present king and his nobles are 
introducing the manners and learning of Western nations 
just as fast as it can be accomplished. The correctness of 
this logic from that fulfilled prediction no one can question. 
The time of the total eclipse of the sun which was visible 
in this country in 1859, fulfilled the calculations within less 
than one' quarter of a minute as to the duration of the total 
obscuration, and almost exactly as to the time of the arrival 
of that total shadow. 

Under all these circumstances, it is not strange that stu- 
dents of the logic of inductive reasoning should have unani- 
mously fixed on this Rule of Prediction as the crucial test 
of inductions. It is a remark that may not be omitted here, 
that this, which all scientists, Mill, Compte, Huxley Tyn- 
dall, and all the rest have agreed upon as a final and con- 
clusive test of a right to human belief, is the very test on 
which the Almighty based his claim to man's faith in him ; 
namely, his ability to predict the future. The field selected 
by Him is not this of inert, unthinking matter, where blind 
force and law work their inexorable results, but that field 
of human science and national history where passion, preju- 
dice, the blood ties of kings, and the affections and hostili- 
ties of peoples play so conspicuous a part. It is the stand- 
ing testimony, available for every generation, that they, 
seeing the prophecies, and the living and dead nations living 
and lying just as was predicted, might know on the same 
scientific grounds that what He spoke was true, just as they 
know that astronomy is true in its theories. What He has 
said of man has the support of every test. It explains every 



THE INTERPRETATION OF DOCUMENTS. 155 

fact offered. It is simple and harmonious, and requires no 
new complexity as facts are added. It is concurred in by 
consciousness, experience, and every available source of 
proof. Every fact demanded by it is forthcoming. Every 
prediction, whose time has arrived, has been and ia now ful- 
filled. Intellectual acceptance of it is, therefore, obligatory 
on the most purely scientific grounds, 

THE INTEEPKETATION OF DOCUMENTS, 

Hitherto we have considered how we may interpret nature. 
The aim has been to read nature'-s laws and classifications. 
Nature is like a building, of which we have no copy of the 
architect's plans and specifications. To learn, therefore, 
what the plan is, resort must be had to the study of the 
building itself. But thought is not merely expressed in 
things done, in machinery constructed, and matters located 
and adjusted with a view ta a given result. Thought may 
also be expressed in language. When the meaning of that 
language is obscure, the same methods of comparison are 
resorted to which we bring to our aid in the interpretation 
of nature. This subject, therefore, of the interpretation of 
documents is closely related to the matters already attended 
to, and is of such importance in the right understanding 
and composition of public papers, especially legal writings, 
that it deserves much attention. While it will be treated 
of here in the light of the Interpretation of Documents, the 
discussion will be equally instructive as to the proper method 
of drawing up such papers. On that last point, however, 
this is to be said in the outset; the perfection of style in the 
composition of all legal papers is such explicitness, that the 
meaning will be evident on the face of the instrument. This 
is presumed to be the ordinary intention of all who use lan- 
guage. It is to express, not to conceal, thought. Hence 
arises the 



156 E VERY-DAY REASONING* 

First Rule of Interpretation* 

The presumption is always strongly in favor of the plain, 06* 
vious meaning of the language. Kent's Commentaries has 
it that " plain, unambiguous words need no interpretation. 
The bulk of mankind act and deal with great simplicity. 
Words are to be taken in their popular, ordinary meaning, 
unless some good reason be assigned to show that they 
should be understood in a different sense." It is to be as- 
sumed that if a writer had meant something different from 
what his language- expresses, he would have changed his 
language. 

In Greenleaf, on Evidence, the following rule from Chan- 
cellor Wigram on the interpretation of wills, is quoted with 
approval, saying there is no material difference in the in- 
terpretation of 'wills and contracts. " Where there is nothing 
in the context of a will from which it is apparent that the 
testator has used the words, in which he has expressed him- 
self, in any other than their strict and primary sense, and 
where his words so interpreted are sensible with reference to 
extrinsic circumstances, it is an inflexible rule of construc- 
tion, that the words of the will shall be interpreted in their 
strict and primary sense, and in no other ; although they 
may be capable of some popular or secondary interpreta- 
tion, and although the most conclusive evidence of intention 
to use them in such popular or secondary sense be tendered." 
The reference in the above extract shows that the context 
of the will and its general language may show that there 
are some peculiarities in its use of words, but the strong pre-, 
sumption is against such use. The whole burden of proof, 
therefore, is on those who ask for any other than the plain 
meaning of the terms. It is a lamentable fact, however, 
that either from persons not knowing what they want to 
say, or not knowing how to say it, there is a vast mass of 
even such plain matters as legal documents, where only the 



THE INTERPRETATION OF DOCUMENTS. 157 

severest simplicity is in place, in which it is next to an 
impossibility to be certain of the intention. A member of 
the London bar, in a work on Civilization as a Science, speaks 
thus : " If on any topic, precision and certainty of language 
are required, they are unquestionably essential 'in the fram- 
ing of laws, where doubt and ambiguity may not only be of 
consequences the most pernicious, but even defeat the very 
aim and purpose of the law itself. The Parliament of this 
nation, having in its august wisdom from time immemorial 
up to the present period, -adopted an exactly opposite prin- 
ciple to the oue here laid down, it is, perhaps, somewhat 
presumptuous, if not actually incurring a high breach of 
privilege, for me to question its soundness. Yet in nearly 
every case doubt and uncertainty have marred our legal 
code, upon whatever subject, owing to the loose and unscien- 
tific construction. Some laws have failed to attain the very 
objects which were specially intended to be brought within 
their scope ; while others have been determined to apply to 
topics with which their framers had no intention of dealing." 
Severe as this criticism is, unless English law-makers are 
better than American, it is not unjust. Add now to this 
the controversies and lawsuits which grow out of contracts 
differently understood, and wills indefinitely 'worded, and 
the necessity for insisting on clear, explicit statements in all 
such documents must be manifest. Past experience, how- 
ever, agrees in asserting that such clearness is not found, 
and is not likely to be found in all cases. This makes 
further rules of interpretation important. 

Second EtJle. 

In all cases of uncertainty and ambiguity, that interpreta- 
tion should be adopted which other circumstances indicate as 
the intention of those who had authority to fix the phraseology 
originally. By those who had authority to fix the phrase- 
ology originally, is meant those whose assent was necessary 
14 



158 E VERY-BAY REASONING. 

give the instrument validity. This includes the legis- 
lators in the ease of laws, the testator in case of wills, and 
both the parties in the case of contracts. The rule further 
limits the inquiry in these outside matters to discovering 
the intention of the parties in using the words they did. 
The rule of law is rigid in excluding all testimony looking 
to an addition to, or change of, the words of the writing, on 
the ground that this would be not interpreting their con- 
tract, but making a contract for them. The design is to 
secure all available aid in understanding their intention, 
who were the authors of the writing, in using the words they 
did. Of course all this presupposes the admitted genuine- 
ness of the document. If there is any doubt on that point, 
that doubt must first be removed. In ancient writings this 
is often a matter of great skill and importance. 

Having, however, fixed on the language of the document, 
and having found that on its face there are different mean- 
ings that may be found in it, there are certain subordinate 
rules to be followed in determining among these various 
meanings which one was that intended by the writer. We 
have, therefore, this 

Third Eule. 

A document is its own best interpreter. Its obscure passages 
are to be construed in harmony with those whose meaning is 
plain. This gives what is called the context its importance. 
Ambiguous words or phrases are made clear by what pre- 
cedes and follows. Words of doubtful meaning in one place 
have their meaning fixed by their use in other places. 
Though men are often inconsistent with themselves, the pre- 
sumption is that they intend to be consistent, and, therefore, 
what they write should be reconciled if possible. To quote 
again from Kent's Commentaries : " The whole instrument is 
to be viewed and compared in all its parts, so that every 
part of it may be made consistent and effectual. Its con* 



THE INTERPRETATION OF DOCUMENTS. 159 

struetion must be reasonable, and according to the subject- 
matter and motive." 

Fourth Kule. 

Tlxe design the author had in view will aid in determining 
what his intention was in using his words. For this reason 
the discussions of legislative bodies are a great help in inter- 
preting laws. They show what vices they intended to sup- 
press, and what rights they sought to protect. . So important 
is this rule in legal matters that it has passed into a maxim, 
that " where the reason of the law ceases, the law ceases." 
In illustration and enforcement of this rule, Blackstone, 
speaking on the interpretation of laws, gives a case put by 
Cicero of a law intended to induce sailors to persevere in 
their efforts to save vessels in danger of shipwreck. The 
law provided that those who forsook a ship in such a time 
should forfeit all property therein, and that the ship and 
lading should belong entirely to those who stayed in it. On 
a given occasion all forsook a ship but one sick passenger, 
who was unable to get away, and when the ship survived 
the storm he claimed the property. It was agreed, however, 
by all the learned that his case was not within the reason 
of the law, and so his claim was not allowed. The same is 
true of other writings. Cicero himself would use one style 
in writing to his son, at school in Greece, on morals, another 
in defending Archias, the poet, and still another in denounc- 
ing Catiline. The Apostle James, in writing against an idle 
faith, would speak of faiih in different language from Paul, 
when the latter was explaining faith and urging its impor- 
tance. When the object of each is kept in view the two 
uses of the word faith are clearly distinct, and there is no 
inconsistency. To show how empty some of the objections 
are which are offered to the New Testament history, an au- 
thor published some historic doubts concerning Napoleon 
Bonaparte, and the style is different from what it would 
have«been otherwise. 



160 EVERY-DAY REASONING. 

Fifth Rule. 

The spirit and temper of the author must be considered. 
Butler, in Hudibras, would expose a vice in a different 
way from Chalmers in his sermons. So the language of 
David in the Psalms is very unlike that of Solomon in 
Proverbs. Moses, in legislating in Leviticus, is moved by 
a different class of feelings from those that moved him in his 
farewell address found in Deuteronomy. A man in writing 
his will would not adopt the same forms of expression that 
he would in leasing a house to his tenant. Webster would 
argue a case' in one way, and Patrick Henry . in another. 
Much importance thus sometimes attaches to a knowledge 
of the life and character of those whose writings we are in- 
terpreting. So where collateral writings are employed, they 
should be the writings of those of like temper and aim, and 
as nearly similarly situated as possible. This last remark 
has also special application to the next rule. 

Sixth Eule. 

The daily language of an author must be understood to un- 
derstand his writings. Merchants use a different set of 
words from mechanics, and every branch of business has a 
large number of words which are peculiar to itself. As no 
one is competent to interpret a Hebrew book who is not a ' 
thorough Hebrew scholar, no more is a man able to interpret 
the will of a carpenter, in bequeathing his tools, who does 
not know the names of the took. For this reason courts ad- 
mit experts to explain the trade and professional words 
found in the contracts and wills of persons of that trade or 
profession. So Blackstone says : " Terms of art or technical 
terms must be taken according to the acceptation of the 
learned in each art, trade, and science." This rule is in one 
sense only another form of the first rule, for these special 
words are still interpreted in their plain meaning, when we 



THE INTERPRETATION OF DOCUMENTS. *161 

become as familiar with them as their author was. Paul 
was a tent-maker by trade, Luke was a physician, Ezra a 
priest, and, remembering these things, we can more readily 
see the force in their language and figures of speech. 

Seventh Rule. 

Documents are to be interpreted in harmony with the sur- 
roundings of their authors. This rule is of great importance 
in studying the writings of those removed from us in time 
and place. A contract for a substantial, comfortable house 
would mean a very different thing in Greenland from what 
it would in Cuba. In our habits, -there is no naturalness 
in the Scripture illustration of the parable of the Ten Vir- 
gins, while in the country and age in which it was writ- 
ten, it was a perfectly familiar suggestion. So wills are 
wholly unintelligible until we know what property, what 
heirs, and what friends the testator had. Horace's Satires 
are only half-appreciated until we become familiar with the 
people, the manners, and the vices of his time. With reference, 
therefore, to both the sixth and seventh rules, it is true, as was 
said under the fifth, when collateral writings are employed 
to illustrate and explain a document, those are of most value 
and weight which were written by those nearest the author in 
language, occupation, country, and time. * 

In the first volume of Greenleaf on Evidence, there is a 
suggestion in explanation of the reason of all these rules 
which is so important that it is quoted here. " In all cases 
in which oral evidence is admitted in exposition of that 
which is written, the principle of admission is that the court 
may be placed, in regard to surrounding circumstances, as 
nearly as- possible in the situation t)f the party whose written 
language is to be interpreted ; the question being, What 
did the person thus circumstanced mean by the language he 
has employed ? " If this is important to a court when it is 
called to construe a document, to the same extent and in the 
14* L 



162 EVERY-DAY REASONING. 

same sense, and for the same reasons, is it important for all 
who seek for the meaning of writings. When we have so 
familiarized ourselves with the style, design, spirit, lan- 
guage, and surroundings of an author that, standing in his 
place, we would use the same words he would, to express the 
same thoughts, we are in the most favorable situation to 
know and explain what the thoughts were which he intended 
to express by the words to be interpreted. 

THE AET OP DEBATE. 

Mankind are so constituted that both physical and intel- 
lectual vigor are attained by exercise. Athletes, gymnasts, 
and racers are examples of that to which the body may be 
brought by suitable discipline. Greatness of mind is not 
less the result of patient and persistent effort. Whoever, 
therefore, would acquire skill in the methods of reasoning, 
must seek it by constant practice. Thus far we have spoken 
mainly in the direction of guiding investigation. The op- 
portunities, however, of exercising ourselves in that kind of 
inductive reasoning do not furnish so easy and simple disci- 
pline as either formal or informal debate. By this last 
method we are brought, in an agreeable manner, to go 
through the intellectual process of testing our inductions, 
and showing whether our suppositions, that they may be 
substantiated by one or more of the four methods, are cor- 
rect or not. It is this mental practice which has made de- 
bating and conversational societies so useful and deservedly 
popular. When those who have made themselves at home 
with these methods and steps of reasoning are called upon 
to advocate or resist any measure in a deliberative assembly, 
their skill so acquired gives them very great advantages. 
In neighborhood meetings, church gatherings, legislative 
halls, judicial trials, and every like place, ability in this di- 
rection, either natural or acquired, is of the utmost practical 



THE ART OF DEBATE. 163 

importance. The following rules, if followed, will aid 
greatly in achieving success. 

First Rule. 

Secure a clear ', exact statement of the question in controversy. 
To do this, get a concise form for the proposition you are to 
advocate. Get an equally distinct statement of the proposi- 
tion they are to maintain who differ from you. It is always 
best where there are to be but two sides, to have the question 
so stated that it can be answered by yes and no, and the 
propositions of the affirmative and negative such that both 
cannot be true or both false, but that one must be true and 
the other false ; so that, proving the falsity of Dne, the truth 
of the other is thereby proved. Unless these conditions are 
complied with, indirect proof will not be available. Indi- 
rect proof is where an assertion is proved by showing the 
falsity of every other supposition. Thus if the question is, 
"Is the mind of man a spiritual existence?" it is good 
proof to show that it is not material. The i.sual method 
adopted by those who assert that all our ideas are acquired 
by experience is to prove that they are not innate, which 
would be valid indirect proof, if it was not for the third sup- 
position, that there are certain principles of intuitive truth 
in the mind to be called into exercise by experience. This 
shows that there are many cases in practical life where it is 
not possible to have such a statement as that recommended 
above for all voluntary debates. In all gatherings where 
resolutions are to be adopted, the variety of fo 'ms proposed 
is sometimes very great. Generally, however, it settles down 
to a very few propositions, from which it is evident the one 
adopted will be taken. In all such cases, as in every case, 
it is of great importance to have these propositions distinctly 
stated, so that there shall be no ambiguous wor s or phrases. 
Oftentimes disputants would agree if they unc.arstood each 
other. By all means, therefore, let the points at issue be 



164 EVERY-DAY REASONING. 

put into the briefest terms and in the most explicit language 
possible. The very object of the pleadings in courts is to 
get into distinct view just what each side claims; and it 
would be w T ell if the like exactness was everywhere adopted. 

Second Kule. 

Having thus obtained a clear view of the whole field of 
controversy, study all sides of the question. It is usually best 
to study the side of those who oppose you first. The mind 
is easily prejudiced in favor of its own opinions. When so 
prejudiced, it cannot correctly weigh the views of others. 
The mind is, therefore, in the most impartial condition at 
the outset of the study, to take in fairly the arguments of 
the opposition. Be assured nothing is gained by underesti- 
mating the strength of an antagonist, just as it displays no 
courage to underrate any peril. Having well studied the 
other side, study your own side in the light of all that can 
be said in opposition thereto. This is the best method of 
providing against unexpected arguments and replies. 

Third Kule. 

Adhere to the real question. Neither advance arguments 
which touch only part of the question, nor be beguiled into 
answering like arguments from the other side. Not unfre- 
quently, iii the discussion of such side-issues, the vital point 
is lost sight of. Proving part of a question is only justifi- 
able when it can be shown that the rest is either admitted or 
independently proved. In such cases, this relation of the 
part proved to the admitted truths, and to the whole ques- 
tion, should be kept prominent. 

Fourth Kule. 

Arrange the arguments, thus gathered, so that they shall mu- 
tually support and enforce each other. Arguments may be 
classed under three heads. Some are available for direct 



THE ART OF DEBATE. 165 

proof, Others for indirect proof, and others for refutation. 
The first class positively proves your position true. The 
second proves every other supposition false. The third de- 
stroys the proofs of the other side. Some arguments may 
bear in two of these ways, and should be so introduced as to 
gain the increased weight of this double force. Many di- 
rect arguments also refute the opposing arguments. When 
a cause is to be upheld, against which a prejudice exists, it is 
usually best to endeavor to allay that prejudice early in the 
argument, either by setting forth arguments likely to be 
received with favor, or by showing that the prejudice is 
groundless. The earlier and last arguments should be the 
strongest. Weak arguments should rarely be used at all ; 
but if used, they should come in the middle of an address, 
giving to strong arguments the posts of honor in making the 
first impressions and last. Sophistry is without excuse or 
rule. 

Fifth Kule! 

Arguments should be presented not only in abstract form, 
but also in the way of concrete illustrations whenever practicable. 
All men see a truth, when a case is put in which that truth 
is involved, more readily and distinctly than when it is 
stated in a mere form of words. Multitudes of mechanical 
inventions look very well in theory, but when made, will not 
work. So it is with many of the arguments we find our- 
selves relying on, and others urging against us. Many people 
cannot see the justice of a claim made against them until 
the case is reversed, and they are in danger of losing by 
it. A gentleman was objecting to* the Bible because he 
could not understand it, and was asked if he believed a dog 
he saw had one ear standing up and the other hanging 
down. He was much puzzled when asked to explain it. 
For popular oratory this ability to put an argument in the 
Bhape of an illustration is of the greatest value. Gough is 



166 E VERY-DAY REASONING. 

said by some to lack logical ability, but it is orily by those 
who think logic must consist in dry abstractions, and so fail 
to recognize the illustrated argument running through the 
ma^s of his anecdotes. 

Sixth Eule. 

In refutation directness and brevity give force and neatness. 
An argument from agreement is refuted by a case of agree- 
ment of the cause with difference of result, or vice versa. An 
argument from difference is refuted by a case of agreement 
in cause or result. The argument from residues is answered 
by showing that when properly understood there is no re- 
siduum, while the argument from concomitant variations is 
overthrown by a case where the variation of the cause or 
effect is not accompanied by a variation of the other. The 
argument from compliance with the tests of induction is 
answered by showing that the proposed conclusion does not 
fully comply with the tests. The more direct and obtrusive 
the force of these replies can be put the better. Often the 
interrogative form is most effective. A politician was once 
dilating on the danger of disunion from which the country 
was saved by the compromise measures of 1850. He was 
asked, if the Union was in such peril, why it was that gov- 
ernment stocks did not fall ? The argument from govern- 
ment credit could not have been put more sharply. 

Seventh Rule. 

An opponent, with whom we are willing to argue, has a right 
to be treated by us with as much respect as we desire to receive 
from him. This requires fair consideration for all his argu- 
ments at their honest weight. It absolutely forbids all per- 
sonalities, and all charges of improper or indirect motives. 
It requires that while we may show fully and strongly the 
evil consequences of any doctrine or policy, we shall not 
charge these evil consequences on the advocates themselves, 



THE ART OF DEBATE. 167 

unless they directly avow them as the expected results. The 
advocates of a really dangerous doctrine may honestly be- 
lieve its tendencies will be beneficial. Their mistake, there- 
fore, is one of judgment, and not one of intention. Bitter- 
ness and severity are only warranted on rare and momentous 
occasions, and should be undertaken only by those whose 
position and ability justify the assumption of some sort of 
championship, and then with the sense of a painful necessity 
in behalf of truth. 

Eighth Eule. 

Self-possession and equanimity of temper are always to be 
maintained. Excitement is seldom favorable to mental ef- 
fort. Usually it takes away the ordinary use of our facul- 
ties. He who in the midst of surprises and questions and 
noise can keep his coolness, has attained a great point in 
making the best out of his case. To see a speaker assailed 
by interruptions, points of order, questions, and explana- 
tions, and find him, with perfect calmness, keep right on 
with his argument, never seriously diverted from the strong 
points he is making, and yet able by a sentence to bring 
to his aid every fact in his knowledge, just as it is 
needed, for answer, reply, or illustration, is a scene to call 
forth our enthusiastic admiration. That power of self-pos- 
session and this instant command of resources, are the ele- 
ments of a great leader in parliamentary bodies. In large 
assemblies and in small, such men carry far more influence 
than their equals otherwise who lack these talents. Bad 
temper is always a confession of weakness and defeat. It is 
a characteristic^ those who argue for victory and not for 
truth, and should be left to that sort of pretenders of a de- 
sire for knowledge. Why should not an honest seeker after 
wisdom be grateful to any one who upsets the arguments by 
which he has been misled ? These deserve our thanks and 
not our anger. 



168 EVERY-DAY REASONING. 

Many other rules might be given, but adherence to these, 
and intelligent practice, with a careful observation of good 
debaters, will bring fair success. Constant practice is the 
main thing. Exercise in analyzing arguments, to determine 
by what Method they are constructed, is of the greatest value. 
It they are our own arguments, this will show us where to 
fortify ourselves. If they are the arguments of our adver- 
saries, it will show us where to assail them. As the crew 
of an oar-boat, for months before a race, train themselves 
with the utmost severity, that they may be ready for the 
struggle, so those who would do their share in guiding the 
affairs of the community, the church, or the state, with 
which they are connected, should not merely contribute 
their unintelligent and awkward efforts when information 
and sound judgment are demanded, but by disciplining 
their powers on minor matters, they should be ready always 
to explain and defend with force and clearness what they 
believe and why. Many of the greatest names in history 
are of those who overcame defects by persistent practice, 
and their achievements are the encouragements to all, espe- 
cially to the young, to persevere, remembering that " what 
has been done can be done again. " No farm, or workshop, 
or office, is too small for experiments in relation to our daily 
affairs, and no home is too humble for an argument. When 
those who class themselves as the common people shall cease 
depending on others for improvements in the methods for 
lightening their toil, and shall, in faith in themselves, adopt 
their specialty with a determination to understand it thor- 
oughly, seeking information by arguing each doubtful point 
with any one likely to give information 'or furnish hints 
which they can follow, all society shall be greatly benefited 
by the upward impulse thus given, but they themselves 
chiefly shall have their self-respect deepened, their mental 
energy quickened, and their lives made worth the living. 



INDEX. 



ACIDS classified by their oxygen, 89. 
Active causes, 41. 
Adhere to the question, 164. 
Adjustment, 104. 
Admissible facts, 128. 
Admission of facts, 126. 
Advantages of private effort, 168. 
Agassiz on classification, 88. 
Agassiz's prediction, 150. 
Agreement, method of, 53. 

Eule of, 57. 

Defect of, 57. 

Basis of, 63. 

Reply to argument from, 166. 
Analysis, what, 91. 

Qualitative, 92. 

Quantitative, 92. 

Relative, 93. 

Proved by synthesis, 95. 

Related to prediction, 151. 
Anthropoid ape, 145. 
Arbitrary classifications, 24. 
Arithmetic, its importance, 9. 
Arrange the arguments, 164. 
Art of debate, 162. 
Astronomy, its early progress, 111. 

1) ACON on induction, 51. 

** Bad temper condemned, 167. 

Bible interpretation, 127. 

Bible predictions, 154. 

Blanks, their formation, rules for, 109. 

Bonaparte's picture, 70. 

Botany, its classifications, 89. 

Linnasan, 133. 

Natural system, 134. 
Brevity effective, 166. 
Burning, what, 61. 
15 



riAUSE defined, 39. 

^ Caused truth and necessary truth, 18. 

Causes vs. Purpose, 104. 

Causes qualities, 29. 

Children's falsehoods, 124. 

Cicero, 159. 

Circle, its area, 67. 

Civilization as a science, 157. 

Classification, 23. 

As related to causes, 30. 

By the four methods, 87. 
Comet, Halley's, 152. 
Communism, 126. 
Concauses, 40. 

Conchology, its classifications, 89. 
Concomitant variations, method of, 70. 

Principles of, 74. 

Inverse variation, 74. 

In social science, 75. 

Rule of, 75. 
Concurrence, rule of, 135. 
Consequences, opponents not chargeable 

with, 166. 
Consilience of inductions, 135. 
Conversational societies, 162. 
Copernican theory, 130. 
Courtesy required, 166. 
Crystallization, 56. 
Cumulative reasoning, 25. 

"FvAILY language in documents, 160. 
*J Darwinism, 126. 
Davy's experiment, 76. 
Debating societies, 162. 
Deception in war, 125. 
Deduction, 147. 
Demonstrative reasoning, 26. 
Peculiarities of, 26. 

169 



170 



INDEX. 



Design, 102. 

In documents, 159. 
Detection of crime, 63. 

Criminals, 139. 

Law, 115. 
Dew, Well's theory of, 79. 
Difference, method of, 58. 

Rule of, 61. 

Basis of, 63. 

Arguments from . answered, 166. 
Difficulties of identifying causes, 42. 
Direct proof, 165. 

Documents interpret themselves, 156. 
Dormant causes, 40. 
" Dry statistics," 111. 

T^CLIPSE of the sun in Siam, 153. 
J-^ Eclipses, succession of, 138. 
Education, 75. 
Efficiency of causes, 34. 
Ellipticity of planetary orbits discov- 
ered, 118. 
Empirical laws, 32. 

Peculiarities of, 34. 
Encke's comet, 66. 
Established laws, 32. 

Peculiarities of. 34. 
Exceptions, their use, 140. 
Experiments, what, 46. 
Explanation of facts, 120. 
Explosion of lamps, 148. 

PACTS always true, 47. 
-*• Facts demanded, 141. 
Facts from imagination, 113. 
facts not inferences, 127. 
Falling bodies, 146. 
Falsehoods, inconsistent, 15. 

Never in things, 13. 

Come from mind, 14. 

Fatal, 16. 
False reasoning is ruinous, 10. 
Farm experiments, 59, 82. 
Final causes, 102. 
'• Fits of easy transmission," 124. 
Four methods illustrated, 76. 
Function, 103. 

p ATHERLNG facts, 111. 

^ Geography vs. Reasoning, 10. 

Cood observerSjtheir characteristics, 113. 



Gough's illustrations, 165. 

Gravitation, 136. 

Greenleaf on Evidence, 156, 161. 

XT ALLEY'S comet, 152. 
-■"*- Hamilton on Light, 143. 
Harmony, rule of, 123. 
Heat, its effect, 71. 
Herschell's works, 52. 
" How " ceases, 100. 
Hypothesis, what, 116. 
Tested, 120. 

TL LUSTRATIONS, important, 165. 
■*■ Imagination in science, 117. 
Imperfect enumeration, 122. 
Importance of truth, 17. 

Honesty of mind, 17, 113. 
Inconsistent facts, 126 
Indirect proof, 165. 
Inexorable action of Nature's forces, 

105. 
Inferences mixed with facts, 114. 
Intention in documents, 157. 
Interpretation of documents, 155. 
Interstellar ether, 66. 
Invisible rays of light, 138. 
Iron working, 63. 



TACOBI'S trial, 125. 
" Junius, 63. 
Jupiter's moons, 65. 



TRENT'S Commentaries, 158, 156. 
"- Kepler's imagination, 118. 
Knowledge needed for induction, 117. 

T AW distinguished from theory and 

-^ hypothesis, 116. 

Law of Nature defined, 30. 

Legal arguments, 124. 

Legal rules on admission of evidence, 

128. 
Legal trials, sufficiency of facts, 144. 
Light, Emission vs. Vibration, 130. 

Time of movement, 65. 

Tyndall on, 137. 
Lightning-rod, 147. 
Limestone, 92. 
Linnsean botany, 133. 
Lithium, 68. 



INDEX. 



171 



VJANURES, 60. 
-^ *- Mariners compass, 147. 
Measurements, important, 110. 
Mechanics and astronomy, 135. 
Medical diagnosis, superficial, 90. 
Medical experiments, 02, 
Mental operations in biology, 126. 
Method, its importance, 107. 
Methods answered, 166. 

Of induction, 51. 

All to be used, 64. 

Illustrated, 76. 
Mill's logic, 53 

Mixed truth and falsehood. 16. 
Modification of hypotheses, 116. 
Motion, laws of, 71. 

TtfATURE'S laws, 30. 

-^ Nature's laws never tentative, 31. 

Nature's offering, 28. 

Necessary vs. Caused truth, 18. 

Neptune discovered, 143. 

Newton's method with gravitation, 73. 

OBSERVATIONS made by all, 111. 
^ Observations, what, 46. 
Obvious meaning of documents, 156 
Operating causes, 40. 
Organic bodies, elements of, 94. 
Oxygen in combustion, 61. 

PHILOSOPHY of the terminal causes, 

*■ 103. 

Photography, 41, 147. 

Physicians, 148. 

Pleadings in court, their object, 164. 

Poisoning by arsenic, 55. 

Possibility proved by one fact, 25. 

Practice, its importance, 162. 

Prediction, rule of, 148. 

"Probabilities" verified, 150. 

Proving part of the question, 164. 

Ptolemaic theory, 130. 

Purpose, 103. 

Purpose vs. Cause, 104. 

QUALITIES, causes, 29. 
Qualities, causes, related to classifi- 
cation, 30. 
Questions of induction, 30, 96. 



ID ATIO of distances and times of plan- 

-"' ets, 118. 

Reading laws in Nat re, 24. 

Reasoning, its impor .mce, 9. 

Its practical utility , 11. 

On necessary trutl. , 21. 

On caused trutl), 21. 
Refutation, what, 165. 
Residues, method of, 65. 

Rule of, 67. 
Rust, 54 

OAUL'S answer to gamuel, 124. 
^ Sciences related to each other, 117. 
Scientific classificatio is, 24. 
Scientific negation, 128. 
Secular inequalities, 40. 
Selection of facts, rules for, 48. 
Self-possession. 167. 
Severity, when allowable, 167. 
Siam, sun's eclipse in, 153. 
Simplicity, rule of, 129, 

In court trials, 129. 
Social science superficial, 90. 
Spirit and temper in locuments, 160. 
State the question clearly, 163. 
Stating the question, 107. 
Steps in induction, 107. 
Strong arguments, where to place, 165. 
Study all sides of the question, 164. 
Style of language in legal documents, 

155. 
Subordinate causes, 40. 
Success, its sources, 168. 
Sufficiency, rule of, 141. 
Surroundings of an author in documents, 

161. 
Suspension bridge, 101. 
Syllogism related to necessary truth, 21. 

In deduction, 146. 
Synthesis, 95. 

rPELEGRAPH, 147. 
■*• Tests, cumulative, 123 
Theory, what, 116. 
Tides, facts needed, CO. 
Trees of lead, 60. 
Truth consistent, 15. 

In things, 13. 

Defined, 13. 

Consistent and harmonious, 125. 



172 



INDEX. 



Truth true of itself, 14. 
Truth w. Falsehood, 13, 
Truth simple, why, 132. 
Tyndall on Light, 137. 

YAR1ATION inverse, 74. 
' Venus's phases, 127, 142. 
Verification, 120. 
Volition in caused truth, 18. 
Vortices, 133. 



WEATHER bureau, 149. 

Weather bureau, facts for, 112. 
Well's theory of dew, 79. 
"What then ? " Whewell's question, 146. 
Whewell'.s works, 52. 

On Light, 131. 
"Why," answerable, 99. 

Always present, 100. 
"Why not?" Whewell's question, 146. 
Witnesses mistaken, 114 
Wooden men for observers, 114. 



THE END. 



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